CA2130290A1 - Process for cladding precious metals to precipitation hardenable materials - Google Patents
Process for cladding precious metals to precipitation hardenable materialsInfo
- Publication number
- CA2130290A1 CA2130290A1 CA002130290A CA2130290A CA2130290A1 CA 2130290 A1 CA2130290 A1 CA 2130290A1 CA 002130290 A CA002130290 A CA 002130290A CA 2130290 A CA2130290 A CA 2130290A CA 2130290 A1 CA2130290 A1 CA 2130290A1
- Authority
- CA
- Canada
- Prior art keywords
- strip
- layer
- temperature
- set forth
- generally
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/08—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of copper or alloys based thereon
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
- B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
- B32B15/018—Layered products comprising a layer of metal all layers being exclusively metallic one layer being formed of a noble metal or a noble metal alloy
Abstract
ABSTRACT OF THE DISCLOSURE
This invention relates to a process for cladding precious metals to precipitation hardenable materials. In accordance with one aspect of the present invention, are the steps of (i) placing a precious metal layer of a first selected thickness atop a selected beryllium-copper alloy base metal strip of a second selected thickness to approximate a desired final product thickness, (ii) cold rolling the layer and strip to reduce their respective thicknesses by generally more than 50%, (iii) heating the layer and strip to a first selected temperature generally within a range of 1000°-1300°F, (iv) maintaining the first temperature for a first selected time to promote metallic bonding of the layer to the strip while softening the base metal, (v) pickling the layer and strip to remove surface oxides, (vi) cold rolling the layer and strip to a thickness generally 11% greater than that of the desired final product thickness, (vii) heating the layer and strip to a second selected temperature generally within a range of 1250°-1400°F, (viii) maintaining the second temperature for a second selected time to effect dissolution of the beryllium into the copper and growth of metallic grains in the alloy to a desired size, with minimal diffusion of the base metal into the precious metal, (ix) pickling bonded strip and layer to remove surface oxides, (x) cold rolling the layer and strip generally to the desired final product thickness, (xi) heating the layer and strip to a third selected temperature generally within a range of 500°-800°F and (xii) maintaining the third temperature for a third selected time to resurrect strength, ductility and conductivity of the base metal.
This invention relates to a process for cladding precious metals to precipitation hardenable materials. In accordance with one aspect of the present invention, are the steps of (i) placing a precious metal layer of a first selected thickness atop a selected beryllium-copper alloy base metal strip of a second selected thickness to approximate a desired final product thickness, (ii) cold rolling the layer and strip to reduce their respective thicknesses by generally more than 50%, (iii) heating the layer and strip to a first selected temperature generally within a range of 1000°-1300°F, (iv) maintaining the first temperature for a first selected time to promote metallic bonding of the layer to the strip while softening the base metal, (v) pickling the layer and strip to remove surface oxides, (vi) cold rolling the layer and strip to a thickness generally 11% greater than that of the desired final product thickness, (vii) heating the layer and strip to a second selected temperature generally within a range of 1250°-1400°F, (viii) maintaining the second temperature for a second selected time to effect dissolution of the beryllium into the copper and growth of metallic grains in the alloy to a desired size, with minimal diffusion of the base metal into the precious metal, (ix) pickling bonded strip and layer to remove surface oxides, (x) cold rolling the layer and strip generally to the desired final product thickness, (xi) heating the layer and strip to a third selected temperature generally within a range of 500°-800°F and (xii) maintaining the third temperature for a third selected time to resurrect strength, ductility and conductivity of the base metal.
Description
7 Field of the Invention The present invention relates to processes for joining precious metals to precipitation hardenable materials and more - particularly to a process for cladding a precious metal to a precipitation hardenable base metal which minimizes use of precinus metal while sustaining strength, ductility and I conductivity of the base metal.
Backqround of the Invention When cladding a precious metal to a precipitation harden-able base metal, thermally induced diffusion (or interdiffusion) between the metals is common. The result is diminished purity of the precious metal. Because interdiffusion is a~ function of temperature, it becsmes significant when cladding w}th base ; metals of relatively high annealing temperatures, e.g., ; 15 beryllium-copper alloys.
To compensate for interdiffusion, substantial amounts of ,...
precious metal have been used in excess of that required for the -, finished product, i.e., electronic connectors. For this reason, beryllium-copper alloys have been found relatively costly for use as a base metal.
:;:
Conventional copper alloys with relatively low annealing ~-temperatures such as phosphor bronze are processed, e.g., by cladding, with minimal interdiffusion. While relatively eco-nomical for use as a base metal, phosphor bronze lacks the strength, ductility and conductivity of beryllium-copper alloys. ~-SummarY of the Invention In accordance with one aspect of the present invention, thexe is provided an improved process for cladding precious -;
metals to beryllium-copper alloys. The process comprises the steps of (i) placing a precious metal layer of a first selected :
thickness atop a selected beryllium-copper alloy base metal u strip of a second selected thickness to approximate a desired final product thickness, (ii) cold rolling the layer and strip ~
to reduce their respective thicknesses by generally more than ~-- 50%, (iii) heating the layer and strip to a first selected temperature generally within a range of 1000-1300F, (iv) maintaining the first temperature for a first selected time to promote metallic bonding of the layer to the strip while soften-ing the base metal, (v) pickling the layer and strip to remove surface oxides, (vi) cold rolling the layer and strip to a thickness generally 11% greater than that of the desired final ;
product thickness, (vii) heating the layer and strip to a ~;~
second selected temperature generally within a range of 1250- ~ ;
1400F, (viii) maintaining the second temperature for a second selected time to effect dissolution of the beryllium into the copper and growth of metallic grains in the alloy to a desired size, with minimal diffusion of the base metal into the precious metal, (ix) pickling the strip and layer to remove surface oxides, (x) cold rolling the layer and strip generally to the ~l desired final product thicXness, (xi) heating the layer and strip to a third selected temperature generally within a range of 500-800F and (xii) maintaining the third temperature for a ``
third selected time to resurrect strength, ductility and con-ductivity of the base metal.
Although the present invention is described in connection with a copper alloy which includes beryllium, it may be adapted ~
for cladding precious metals to other precipitation hardenablP ~ ;
materials such as alloys of nickel, titanium and iron.
Accordingly, it is an object of the present invention to clad a precious metal to a beryllium copper alloy base metal `
with minima:L consumption o~ precious metal while preserving strength, ductility and conductivity of the base metal.
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Another object of the present invention is to provide for the simple, efficient and economical manufacture of precious metal clad beryllium-copper alloy strip products.
still another object of the present invention is to clad precious metals to beryllium-copper alloys at relatively low process temperatures to reduce interdiffusion.
Still other objects and advantages of the present invention will become apparent from the following description of the pre-ferred embodiments.
Brief Description of the Drawings -~
FIG. 1 is a perspective view of a section of precious metal clad beryllium-copper strip product, in accordance with one aspect of the present invention; and i FIG. 2 is a sectional view taken along line 2-2 of PIG. 1 ~`
showing the respective layers of the strip product. The same ~ numerals are used throughout the figure drawings to designate ¦~ similar elements. -~
~ Detailed Descri~tion of the Preferred Embodiments .
Precipitation hardenable materials of high strength, duc-tility and conductivity such as beryllium-copper alloys have been found desirable for use as base metals in electronic connectors, e.g., for automobiles and the like. Because conventional methods of electroplating (or cladding) phosphor bronze with precious metals are performed with relatively little interdiffusion, beryllium-copper alloys have been generally less :
economical for commercial use.
It has been found, howev~r, that by using annealing temperatures notably lower and for longer times than those of conventional processes, interdiffusion between precious metals and beryllium-copper alloys is reduced exponentially. Less :
- 4 - ~
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precious metal is then required to produce the finished product, lowering costs.
In accordance with one aspect of the present invention, there is provided an improved process for cladding precious metals to beryllium-copper alloy base metals. The process comprises the steps of (i) placing a precious metal layer of a :~.
first selected thickness atop a selected beryllium-copper alloy base metal strip of a second selected thickness to approximate a desired final product thickness, (ii) roll bonding the layer to .
the str.ip to reduce their respective initial thicknesses by ; generally more than 50%, (iii) heating the layer and strip to a first selected temperature generally within a range of 1000-1300F, (iv) maintaining the first temperature for a first ~
selected time to promote metallic bonding of the layer to the ~-strip while softening the base metal, (v) pickling the layer and ~:~
strip to remove surface oxides, (vi) roll bonding the layer to ..
the strip to a thickness generally ~1% greater than that of the : desired final product thickness, (vii) heating the layer and strip to a second selected temperature generally within a range ~.
of 1250-1400F, (viii) maintaining the second temperature for .:;
a second selected time to effect dissolution of the beryllium ~ into the copper and growth of metallic grains in the alloy to a -~
i~ desired size, with minimal diffusion of the base metal into the ~-;~ precious metal, ~ix) pickling the strip and layer to remove surface oxides, (x) roll bondinq the layar to the strip gener~
: - ~
ally to the desired final product thickness, (xi) heating the layer and strip to a third selected temperature generally within a range of 500-800F and (xii) ma.intaining the third tempera- ;~
ture for a third selected time to resurrect strength, ductility and conductivity of the base metal.
Referring now to FIGS. 1 and 2, there is shown generally a precious metal clad beryllium-copper alloy strip product 10. To - 5 - .~
' . .
:
achieve a product having, for example, a base metal 0.010 inch thick 1/4 HM in beryllium-copper alloy with 0.00003 inch thick nominal precious metal thickness, a stripe of precious metal 20 i5 layered initially to a first selected thickness, e.g., about 0.000197 inch, upon one edge of a beryllium-copper alloy base metal strip 40 of a second selected thickness, e.g., approxi~
mately 0.062 inch. The thicknesses are selected depending on device, function and specificatlons, as will be appreciated by those skilled in the art.
Precious metal stripe 20 is preferably a layered composite which comprises a layer 21 of gold joined, e.g., by cladding, to layer 22 of palladium or palladium alloy. Examples include a palladium-silver alloy containing about 60% palladium and about 40% silver and a palladium-nickel alloy of about 80% palladium and about 20% nickel.
Next, a first bonding step is performed. During this step, ; the precious metal layer is roll bonded to the base metal strip, ~;`
e.g., preferably by cold rolling, reducing their respective in-itial thicknesses by generally less than 50%. In the present example, the base metal strip is reduced in thickness from ;~
approximately 0.062 inch to 0.0285 inch. The precious metal thickness is reduced proportionately.
A~ best seen in FIG. 2, a diffusion barrier 30 such as a ~, ! layer of nickel is placed between base metal strip 40 and preci-ous metal stripe 20 to further reduce interdiffusion between the bonded layers. In an alternative embodiment, the diffusion barrier is omitted.
In accordance with one aspect of the present invention, cold rolling is per~ormed using a rolling mill. The mill has rotating rolls which are separated by a selected distance from one another, the distance corresponding to the desired thickness of the strip product. Operating temperatures are generally u below that which would soften the materials to be cold rolled.
For instance, with beryllium-copper alloys, the maximum process temperature is around 200F. Preferably, a lubricating oil is `-- used during cold rolling to maintain a uniform surface finish and extract heat.
During a first heating phase, the bonded precious metal layer and beryllium~copper alloy base metal are heated to a ~
first temperature generally within a range of 1000-1300F. `
A temperature of 1150F has been found suitable. This tempera- -~
; 10 ture is maintained for a first selected time, e.g., about 3-5 minutes, sufficient to soften the base metal and promote metal-lic bonding of the precious metal layer to the base metal strip. ;~
.
Suitable first temperatures are as much as about 250F -~
below those of conventional processes for cladding beryllium-copper alloys, for example, 1450-1550F. By lowering the ~
temperature, interdiffusion between the precious metal and ~-beryllium-copper alloy is decreased, thereby reducing precious metal requirements. Because less precious metal is needed, the ~ , ,.
~; ; present invention advantageously provides cost effective pro-;~ 20 duction of precious metal clad beryllium-copper alloy strip :
products.
As an intermediate step, the layer and strip are pickled, ~ : .
preferably in a bath of either sulfuric or nitric acid, to remove oxides from base metal surfaces which typically develop during high temperature annealing operations. The pickling process preferably involves one or more pre-pickling stages followed by a bright pickle stage. During the pre-pickle stage(s), the layer and strip are immersed in a first hot ~ -acid solution, e.g., 20% to 30% sulfuric acid at a temperature generally within a range of 150-180F. Alternatively, a , solution of caustic soda is used.
The bright pickle stage then utilizes a second hot acld solution, e.g., about 15% to 20% nitric acid at a temperature ranging generally from room temperature to about 100F. Alter-natively, the acid solution comprises around 20% to 30% sulfuric acid at a temperature ranging generally from room temperature to about 150F. After each stage, the layer and strip are immersed in rinsing and neutralizing solutions, as is known by those skilled in the art.
During the next step of the present invention, the bonded precious metal layer and beryllium-copper alloy base metal strip are again roll bonded to one another, e.g., preferably by cold ~ rolling, but this time to a combined thickness generally 11%
¦ greater than that of the final product, e.g., about 0.011 inch.
A second heating phase is then performed. During this phase, the bonded layer and base metal are exposed to a second selected temperature generally within a range of 1250-1400F.
Like the first heating phase, the second temperature is sub-stantially lower than those temperatures used during conven-;~ tional processing of~beryllium copper alloys, such as 1450F.
The objective, again, is to reduce precious metal requirements by decreasing the amount of interdiffusion between the precious ~; metal and beryllium-copper alloy.
This second temperature, e.g., about 1350F, is maintained for a second selected time sufficient to cause dissolution of J ! . ~ , ~ 25 beryllium into copper (within the beryllium-copper alloy) and : ~
growth of the alloy's metallic grains to a size desirable for ~; selected mechanical properties, i.e., strength, ductility and conductivity. It will be understood, however, by those skilled in the art that the duration of heating is not so long as to cause significant diffusion of the base metal into the precious metal. A second selected time of generally 1-3 minutes has been found suitable.
:::
` - 8 -The bonded precious metal layer and base metal are again ;
pickled in acid to remove metal oxides from the metal surface -which may develop during heating, and roll bonded, e.g., by cold rolling, this time to a final product thickness, such as 0.010032 inch.
Finally, the bonded layer and base metal strip are heated to a third selected temperature generally within a range of 1 500-800F. The third temperature, e.g., approximately 700F, ¦ is maintained for a third selected time, up to about 4 hours, ¦~ 10 sufficient to develop the desired mechanical properties in the i strip product, such as strength (hardness), ductility and conductivity.
A variety of tests have been conducted using the present process. Representative examples are set forth below.
~ ~ ''' '' '.'`' Base Metal Start Thickness 0.060 inch Beryllium Content l.9O weight %
;~ Precious Metal Start Thickness 0.000360 inch total 1~ (0.000040 inch Au) (0.000320 inch Pd-Ag alloy) ~; Roll Bonding 0.060 to 0.028 inch Annealing 1300F for 2 min.
Pickling sulfuric acid bath ~ Cold Rolling 0.0280 to 0.0112 inch `~ 25 Annealing 1300F for 4 min.
Pickling sulfuric acid bath ~1 Cold Rolling 0.0112 to 0.0100 inch Annealing 700F for 10 min.
Base Metal Final Thickness 0.0100 inch Ultimate Tensile Strength 130 ksi 0.2 ~ Offset Yield Strength 108 ksi Elongation in 2" 14 Electrical Conductivity 21.2 % IACS
% Stress Remaining after 1000 hours ~ 125C 90 Precious Metal Final Thickness 0.000056 inch total (0 000006 inch Au) (0 000050 inch Pd-Ag alloy) .! -:
.:
l ' _ 9 _ ~' ;' '."'''' ':', .~
Initial Contact Resistance 4.3 milliohms Contact Resistance - 1000 hours Measured at 150C 3.7 milliohms Measured at 200C 3.7 milliohms Base Metal Start Thickness 0.054 inch Beryllium Content 1.76 weiyht ~
Precious Metal Start Thickness 0.000204 inch total (0.000021 inch Au) (0.000183 inch Pd-Ag alloy) Roll Bonding 0.054 to 0.018 inch Annealing 1300F for 2 min.
Pickling sulfuric acid bath Cold Rolling 0.0180 to 0.01121inch Annealing 1350F for 3.3 m!in.
Pickling sulfuric acid bath Cold Rolling 0.0112 to 0.0100 inch ;~ Annealing 725F for 4 min.
Base Metal Final Thickness 0.0100 inch Ultimate Tensile Strength 118 ksi ~ 0.2 ~ Offset Yield Strength 97.3 ksi ; % Elongation in 2" 17 Electrical Conductivity 21.5 ~ IACS
% Stress Remaining after 1000 hours @ 125C 87 Precious Metal Final Thickness 0.000190 inch total (0.000035 inch Au) ; (0.000155 inch Pd-Ag alloy) Initial Contact Resistance 1.5 milliohms :~ :
Contact Resistance - 1000 hours ' ~ Measurediat 150C 3.0 milIiohms Measured at 200C 3.0 milliohms Again, by using annealing temperatures notably lower than those of conventional processes, the coefficient of diffusion (or interdiffusion) between the precious metal layer and the ~;
base metal is reduced exponentially. This results in a sub-stantial reduction in the precious metal needed to produce the finished strip product, lowering costs. In this manner, the ~'`.
- 10 - ``, present process advantageously produces strip products of pre~
cious metal clad beryllium-copper alloy of desired physical and mechanical properties, e.g., those within standard published temper designations, but at a significantly lower cost than conventional methods.
Although the embodiments illustrated herein have been described for use with a beryllium-copper alloy, an equivalent ~
process could be practiced on other precipitation hardenable -¦ materials such as alloys of nickel, titanium or iron, giving consideration to the purpose for which the present invention is intended. Similarly, precious metals and their alloys other than those of gold or silver may be clad to beryllium-copper alloys or other suitable precipitation hardenable materials.
Various modifications and alterations to the present invention may be appreciated based on a review of this ~ ~-disclosure. These changes and additions are intended to be within the spirit and scope of the invention as defined by the following claims.
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~ ~ ' : ,' ~ ';' - .
.,',..,~
Backqround of the Invention When cladding a precious metal to a precipitation harden-able base metal, thermally induced diffusion (or interdiffusion) between the metals is common. The result is diminished purity of the precious metal. Because interdiffusion is a~ function of temperature, it becsmes significant when cladding w}th base ; metals of relatively high annealing temperatures, e.g., ; 15 beryllium-copper alloys.
To compensate for interdiffusion, substantial amounts of ,...
precious metal have been used in excess of that required for the -, finished product, i.e., electronic connectors. For this reason, beryllium-copper alloys have been found relatively costly for use as a base metal.
:;:
Conventional copper alloys with relatively low annealing ~-temperatures such as phosphor bronze are processed, e.g., by cladding, with minimal interdiffusion. While relatively eco-nomical for use as a base metal, phosphor bronze lacks the strength, ductility and conductivity of beryllium-copper alloys. ~-SummarY of the Invention In accordance with one aspect of the present invention, thexe is provided an improved process for cladding precious -;
metals to beryllium-copper alloys. The process comprises the steps of (i) placing a precious metal layer of a first selected :
thickness atop a selected beryllium-copper alloy base metal u strip of a second selected thickness to approximate a desired final product thickness, (ii) cold rolling the layer and strip ~
to reduce their respective thicknesses by generally more than ~-- 50%, (iii) heating the layer and strip to a first selected temperature generally within a range of 1000-1300F, (iv) maintaining the first temperature for a first selected time to promote metallic bonding of the layer to the strip while soften-ing the base metal, (v) pickling the layer and strip to remove surface oxides, (vi) cold rolling the layer and strip to a thickness generally 11% greater than that of the desired final ;
product thickness, (vii) heating the layer and strip to a ~;~
second selected temperature generally within a range of 1250- ~ ;
1400F, (viii) maintaining the second temperature for a second selected time to effect dissolution of the beryllium into the copper and growth of metallic grains in the alloy to a desired size, with minimal diffusion of the base metal into the precious metal, (ix) pickling the strip and layer to remove surface oxides, (x) cold rolling the layer and strip generally to the ~l desired final product thicXness, (xi) heating the layer and strip to a third selected temperature generally within a range of 500-800F and (xii) maintaining the third temperature for a ``
third selected time to resurrect strength, ductility and con-ductivity of the base metal.
Although the present invention is described in connection with a copper alloy which includes beryllium, it may be adapted ~
for cladding precious metals to other precipitation hardenablP ~ ;
materials such as alloys of nickel, titanium and iron.
Accordingly, it is an object of the present invention to clad a precious metal to a beryllium copper alloy base metal `
with minima:L consumption o~ precious metal while preserving strength, ductility and conductivity of the base metal.
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Another object of the present invention is to provide for the simple, efficient and economical manufacture of precious metal clad beryllium-copper alloy strip products.
still another object of the present invention is to clad precious metals to beryllium-copper alloys at relatively low process temperatures to reduce interdiffusion.
Still other objects and advantages of the present invention will become apparent from the following description of the pre-ferred embodiments.
Brief Description of the Drawings -~
FIG. 1 is a perspective view of a section of precious metal clad beryllium-copper strip product, in accordance with one aspect of the present invention; and i FIG. 2 is a sectional view taken along line 2-2 of PIG. 1 ~`
showing the respective layers of the strip product. The same ~ numerals are used throughout the figure drawings to designate ¦~ similar elements. -~
~ Detailed Descri~tion of the Preferred Embodiments .
Precipitation hardenable materials of high strength, duc-tility and conductivity such as beryllium-copper alloys have been found desirable for use as base metals in electronic connectors, e.g., for automobiles and the like. Because conventional methods of electroplating (or cladding) phosphor bronze with precious metals are performed with relatively little interdiffusion, beryllium-copper alloys have been generally less :
economical for commercial use.
It has been found, howev~r, that by using annealing temperatures notably lower and for longer times than those of conventional processes, interdiffusion between precious metals and beryllium-copper alloys is reduced exponentially. Less :
- 4 - ~
~v~
precious metal is then required to produce the finished product, lowering costs.
In accordance with one aspect of the present invention, there is provided an improved process for cladding precious metals to beryllium-copper alloy base metals. The process comprises the steps of (i) placing a precious metal layer of a :~.
first selected thickness atop a selected beryllium-copper alloy base metal strip of a second selected thickness to approximate a desired final product thickness, (ii) roll bonding the layer to .
the str.ip to reduce their respective initial thicknesses by ; generally more than 50%, (iii) heating the layer and strip to a first selected temperature generally within a range of 1000-1300F, (iv) maintaining the first temperature for a first ~
selected time to promote metallic bonding of the layer to the ~-strip while softening the base metal, (v) pickling the layer and ~:~
strip to remove surface oxides, (vi) roll bonding the layer to ..
the strip to a thickness generally ~1% greater than that of the : desired final product thickness, (vii) heating the layer and strip to a second selected temperature generally within a range ~.
of 1250-1400F, (viii) maintaining the second temperature for .:;
a second selected time to effect dissolution of the beryllium ~ into the copper and growth of metallic grains in the alloy to a -~
i~ desired size, with minimal diffusion of the base metal into the ~-;~ precious metal, ~ix) pickling the strip and layer to remove surface oxides, (x) roll bondinq the layar to the strip gener~
: - ~
ally to the desired final product thickness, (xi) heating the layer and strip to a third selected temperature generally within a range of 500-800F and (xii) ma.intaining the third tempera- ;~
ture for a third selected time to resurrect strength, ductility and conductivity of the base metal.
Referring now to FIGS. 1 and 2, there is shown generally a precious metal clad beryllium-copper alloy strip product 10. To - 5 - .~
' . .
:
achieve a product having, for example, a base metal 0.010 inch thick 1/4 HM in beryllium-copper alloy with 0.00003 inch thick nominal precious metal thickness, a stripe of precious metal 20 i5 layered initially to a first selected thickness, e.g., about 0.000197 inch, upon one edge of a beryllium-copper alloy base metal strip 40 of a second selected thickness, e.g., approxi~
mately 0.062 inch. The thicknesses are selected depending on device, function and specificatlons, as will be appreciated by those skilled in the art.
Precious metal stripe 20 is preferably a layered composite which comprises a layer 21 of gold joined, e.g., by cladding, to layer 22 of palladium or palladium alloy. Examples include a palladium-silver alloy containing about 60% palladium and about 40% silver and a palladium-nickel alloy of about 80% palladium and about 20% nickel.
Next, a first bonding step is performed. During this step, ; the precious metal layer is roll bonded to the base metal strip, ~;`
e.g., preferably by cold rolling, reducing their respective in-itial thicknesses by generally less than 50%. In the present example, the base metal strip is reduced in thickness from ;~
approximately 0.062 inch to 0.0285 inch. The precious metal thickness is reduced proportionately.
A~ best seen in FIG. 2, a diffusion barrier 30 such as a ~, ! layer of nickel is placed between base metal strip 40 and preci-ous metal stripe 20 to further reduce interdiffusion between the bonded layers. In an alternative embodiment, the diffusion barrier is omitted.
In accordance with one aspect of the present invention, cold rolling is per~ormed using a rolling mill. The mill has rotating rolls which are separated by a selected distance from one another, the distance corresponding to the desired thickness of the strip product. Operating temperatures are generally u below that which would soften the materials to be cold rolled.
For instance, with beryllium-copper alloys, the maximum process temperature is around 200F. Preferably, a lubricating oil is `-- used during cold rolling to maintain a uniform surface finish and extract heat.
During a first heating phase, the bonded precious metal layer and beryllium~copper alloy base metal are heated to a ~
first temperature generally within a range of 1000-1300F. `
A temperature of 1150F has been found suitable. This tempera- -~
; 10 ture is maintained for a first selected time, e.g., about 3-5 minutes, sufficient to soften the base metal and promote metal-lic bonding of the precious metal layer to the base metal strip. ;~
.
Suitable first temperatures are as much as about 250F -~
below those of conventional processes for cladding beryllium-copper alloys, for example, 1450-1550F. By lowering the ~
temperature, interdiffusion between the precious metal and ~-beryllium-copper alloy is decreased, thereby reducing precious metal requirements. Because less precious metal is needed, the ~ , ,.
~; ; present invention advantageously provides cost effective pro-;~ 20 duction of precious metal clad beryllium-copper alloy strip :
products.
As an intermediate step, the layer and strip are pickled, ~ : .
preferably in a bath of either sulfuric or nitric acid, to remove oxides from base metal surfaces which typically develop during high temperature annealing operations. The pickling process preferably involves one or more pre-pickling stages followed by a bright pickle stage. During the pre-pickle stage(s), the layer and strip are immersed in a first hot ~ -acid solution, e.g., 20% to 30% sulfuric acid at a temperature generally within a range of 150-180F. Alternatively, a , solution of caustic soda is used.
The bright pickle stage then utilizes a second hot acld solution, e.g., about 15% to 20% nitric acid at a temperature ranging generally from room temperature to about 100F. Alter-natively, the acid solution comprises around 20% to 30% sulfuric acid at a temperature ranging generally from room temperature to about 150F. After each stage, the layer and strip are immersed in rinsing and neutralizing solutions, as is known by those skilled in the art.
During the next step of the present invention, the bonded precious metal layer and beryllium-copper alloy base metal strip are again roll bonded to one another, e.g., preferably by cold ~ rolling, but this time to a combined thickness generally 11%
¦ greater than that of the final product, e.g., about 0.011 inch.
A second heating phase is then performed. During this phase, the bonded layer and base metal are exposed to a second selected temperature generally within a range of 1250-1400F.
Like the first heating phase, the second temperature is sub-stantially lower than those temperatures used during conven-;~ tional processing of~beryllium copper alloys, such as 1450F.
The objective, again, is to reduce precious metal requirements by decreasing the amount of interdiffusion between the precious ~; metal and beryllium-copper alloy.
This second temperature, e.g., about 1350F, is maintained for a second selected time sufficient to cause dissolution of J ! . ~ , ~ 25 beryllium into copper (within the beryllium-copper alloy) and : ~
growth of the alloy's metallic grains to a size desirable for ~; selected mechanical properties, i.e., strength, ductility and conductivity. It will be understood, however, by those skilled in the art that the duration of heating is not so long as to cause significant diffusion of the base metal into the precious metal. A second selected time of generally 1-3 minutes has been found suitable.
:::
` - 8 -The bonded precious metal layer and base metal are again ;
pickled in acid to remove metal oxides from the metal surface -which may develop during heating, and roll bonded, e.g., by cold rolling, this time to a final product thickness, such as 0.010032 inch.
Finally, the bonded layer and base metal strip are heated to a third selected temperature generally within a range of 1 500-800F. The third temperature, e.g., approximately 700F, ¦ is maintained for a third selected time, up to about 4 hours, ¦~ 10 sufficient to develop the desired mechanical properties in the i strip product, such as strength (hardness), ductility and conductivity.
A variety of tests have been conducted using the present process. Representative examples are set forth below.
~ ~ ''' '' '.'`' Base Metal Start Thickness 0.060 inch Beryllium Content l.9O weight %
;~ Precious Metal Start Thickness 0.000360 inch total 1~ (0.000040 inch Au) (0.000320 inch Pd-Ag alloy) ~; Roll Bonding 0.060 to 0.028 inch Annealing 1300F for 2 min.
Pickling sulfuric acid bath ~ Cold Rolling 0.0280 to 0.0112 inch `~ 25 Annealing 1300F for 4 min.
Pickling sulfuric acid bath ~1 Cold Rolling 0.0112 to 0.0100 inch Annealing 700F for 10 min.
Base Metal Final Thickness 0.0100 inch Ultimate Tensile Strength 130 ksi 0.2 ~ Offset Yield Strength 108 ksi Elongation in 2" 14 Electrical Conductivity 21.2 % IACS
% Stress Remaining after 1000 hours ~ 125C 90 Precious Metal Final Thickness 0.000056 inch total (0 000006 inch Au) (0 000050 inch Pd-Ag alloy) .! -:
.:
l ' _ 9 _ ~' ;' '."'''' ':', .~
Initial Contact Resistance 4.3 milliohms Contact Resistance - 1000 hours Measured at 150C 3.7 milliohms Measured at 200C 3.7 milliohms Base Metal Start Thickness 0.054 inch Beryllium Content 1.76 weiyht ~
Precious Metal Start Thickness 0.000204 inch total (0.000021 inch Au) (0.000183 inch Pd-Ag alloy) Roll Bonding 0.054 to 0.018 inch Annealing 1300F for 2 min.
Pickling sulfuric acid bath Cold Rolling 0.0180 to 0.01121inch Annealing 1350F for 3.3 m!in.
Pickling sulfuric acid bath Cold Rolling 0.0112 to 0.0100 inch ;~ Annealing 725F for 4 min.
Base Metal Final Thickness 0.0100 inch Ultimate Tensile Strength 118 ksi ~ 0.2 ~ Offset Yield Strength 97.3 ksi ; % Elongation in 2" 17 Electrical Conductivity 21.5 ~ IACS
% Stress Remaining after 1000 hours @ 125C 87 Precious Metal Final Thickness 0.000190 inch total (0.000035 inch Au) ; (0.000155 inch Pd-Ag alloy) Initial Contact Resistance 1.5 milliohms :~ :
Contact Resistance - 1000 hours ' ~ Measurediat 150C 3.0 milIiohms Measured at 200C 3.0 milliohms Again, by using annealing temperatures notably lower than those of conventional processes, the coefficient of diffusion (or interdiffusion) between the precious metal layer and the ~;
base metal is reduced exponentially. This results in a sub-stantial reduction in the precious metal needed to produce the finished strip product, lowering costs. In this manner, the ~'`.
- 10 - ``, present process advantageously produces strip products of pre~
cious metal clad beryllium-copper alloy of desired physical and mechanical properties, e.g., those within standard published temper designations, but at a significantly lower cost than conventional methods.
Although the embodiments illustrated herein have been described for use with a beryllium-copper alloy, an equivalent ~
process could be practiced on other precipitation hardenable -¦ materials such as alloys of nickel, titanium or iron, giving consideration to the purpose for which the present invention is intended. Similarly, precious metals and their alloys other than those of gold or silver may be clad to beryllium-copper alloys or other suitable precipitation hardenable materials.
Various modifications and alterations to the present invention may be appreciated based on a review of this ~ ~-disclosure. These changes and additions are intended to be within the spirit and scope of the invention as defined by the following claims.
- ..
'' ::
.
! : :.
~ ~ ' : ,' ~ ';' - .
.,',..,~
Claims (25)
1. A process for cladding precious metals to precipi-tation hardenable materials, which comprises the steps of:
(a) placing a precious metal layer of a first selected thickness atop a selected precipitation hardenable base metal strip of a second selected thickness to approximate a desired final product thickness;
(b) roll bonding the layer to the strip;
(c) heating the layer and strip to a first selected temperature;
(d) maintaining the first temperature for a first selected time to promote metallic bonding of the layer to the strip while softening the base metal;
(e) pickling the layer and strip to remove surface oxides;
(f) roll bonding the layer to the strip;
(g) heating the layer and strip to a second selected temperature;
(h) maintaining the second temperature for a second se-lected time to effect dissolution of one constituent of the precipitation hardenable material into another and growth of metallic grains in the material to a desired size, with minimal diffusion of the base metal into the precious metal;
(i) pickling the strip and layer to remove surface oxides;
(j) roll bonding the layer to the strip generally to the desired final product thickness;
(k) heating the layer and strip to a third selected temperature; and (l) maintaining the third temperature for a third selected time to resurrect strength, ductility and conductivity of the base metal.
(a) placing a precious metal layer of a first selected thickness atop a selected precipitation hardenable base metal strip of a second selected thickness to approximate a desired final product thickness;
(b) roll bonding the layer to the strip;
(c) heating the layer and strip to a first selected temperature;
(d) maintaining the first temperature for a first selected time to promote metallic bonding of the layer to the strip while softening the base metal;
(e) pickling the layer and strip to remove surface oxides;
(f) roll bonding the layer to the strip;
(g) heating the layer and strip to a second selected temperature;
(h) maintaining the second temperature for a second se-lected time to effect dissolution of one constituent of the precipitation hardenable material into another and growth of metallic grains in the material to a desired size, with minimal diffusion of the base metal into the precious metal;
(i) pickling the strip and layer to remove surface oxides;
(j) roll bonding the layer to the strip generally to the desired final product thickness;
(k) heating the layer and strip to a third selected temperature; and (l) maintaining the third temperature for a third selected time to resurrect strength, ductility and conductivity of the base metal.
2. The process set forth in claim 1 wherein the precip-itation hardenable material comprises an alloy of copper which contains beryllium.
3. The process set forth in claim 1 wherein the first selected temperature is generally within the range of 1000°-1300°F.
4. The process set forth in claim 1 wherein the second selected temperature is generally within the range of 1250°-1400°F.
5. The process set forth in claim 1 wherein the third selected temperature is generally within the range of 500°-800°F.
6. The process set forth in claim 1 wherein step (b) comprises the step of cold rolling.
7. The process set forth in claim 1 wherein step (f) comprises the step of cold rolling.
8. The process set forth in claim 1 wherein step (j) comprises the step of cold rolling.
9. The process set forth in claim 1 wherein the precious metal comprises gold.
10. The process set forth in claim 1 wherein the precious metal comprises silver.
11. A process for cladding precious metals to precipi-tation hardenable materials, which comprises the steps of:
(a) placing a precious metal layer of a first selected thickness atop a selected beryllium-copper alloy base metal strip of a second selected thickness to approx-imate a desired final product thickness;
(b) roll bonding the layer to the strip;
(c) heating the layer and strip to a first selected temperature;
(d) maintaining the first temperature for a first selected time to promote metallic bonding of the layer to the strip while softening the base metal;
(e) pickling the layer and strip to remove surface oxides;
(f) roll bonding the layer to the strip;
(g) heating the layer and strip to a second selected temperature;
(h) maintaining the second temperature for a second selected time to effect dissolution of the beryllium into the copper and growth of metallic grains in the alloy to a desired size, with minimal diffusion of the base metal into the precious metal;
(i) pickling the strip and layer to remove surface oxides;
(j) roll bonding the layer to the strip generally to the desired final product thickness;
(k) heating the layer and strip to a third selected temperature; and (l) maintaining the third temperature for a third selected time to resurrect strength, ductility and conductivity of the base metal.
(a) placing a precious metal layer of a first selected thickness atop a selected beryllium-copper alloy base metal strip of a second selected thickness to approx-imate a desired final product thickness;
(b) roll bonding the layer to the strip;
(c) heating the layer and strip to a first selected temperature;
(d) maintaining the first temperature for a first selected time to promote metallic bonding of the layer to the strip while softening the base metal;
(e) pickling the layer and strip to remove surface oxides;
(f) roll bonding the layer to the strip;
(g) heating the layer and strip to a second selected temperature;
(h) maintaining the second temperature for a second selected time to effect dissolution of the beryllium into the copper and growth of metallic grains in the alloy to a desired size, with minimal diffusion of the base metal into the precious metal;
(i) pickling the strip and layer to remove surface oxides;
(j) roll bonding the layer to the strip generally to the desired final product thickness;
(k) heating the layer and strip to a third selected temperature; and (l) maintaining the third temperature for a third selected time to resurrect strength, ductility and conductivity of the base metal.
12. The process set forth in claim 11 wherein the first selected temperature is generally within the range of 1000°-1300°F.
13. The process set forth in claim 11 wherein the second selected temperature is generally within the range of 1250°-1400°F.
14. The process set forth in claim 11 wherein the third selected temperature is generally within the range of 500°-800°F.
15. The process set forth in claim 11 wherein step (b) comprises the step of cold rolling.
16. The process set forth in claim 11 wherein step (f) comprises the step of cold rolling.
17. The process set forth in claim 11 wherein step (j) comprises the step of cold rolling.
18. The process set forth in claim 11 wherein the precious metal comprises gold.
19. The process set forth in claim 11 wherein the precious metal comprises silver.
20. A process for cladding precious metals to beryllium-copper alloys, which comprises the steps of:
(a) placing a precious metal layer of a first selected thickness atop a selected beryllium-copper alloy base metal strip of a second selected thickness to approximate a desired final product thickness;
(b) roll bonding the layer to the strip to reduce their respective thicknesses by generally more than 50%;
(c) heating the layer and strip to a first selected temperature generally within a range of 1000°- 1300°F;
(d) maintaining the first temperature for a first selected time to promote metallic bonding of the layer to the strip while softening the base metal;
(e) pickling the layer and strip to remove surface oxides;
(f) roll bonding the layer to the strip to a thickness generally 11% greater than that of the desired final product thickness;
(g) heating the layer and strip to a second selected tem-perature generally within a range of 1250°-1400°F;
(h) maintaining the second temperature for a second selected time to effect dissolution of the beryllium into the copper and growth of metallic grains in the alloy to a desired size, with minimal diffusion of the base metal into the precious metal;
(i) pickling the strip and layer to remove surface oxides;
(j) roll bonding the layer to the strip generally to the desired final product thickness;
(k) heating the layer and strip to a third selected tem-perature generally within a range of 500°-800° F; and (l) maintaining the third temperature for a third selected time to resurrect strength, ductility and conductivity of the base metal.
(a) placing a precious metal layer of a first selected thickness atop a selected beryllium-copper alloy base metal strip of a second selected thickness to approximate a desired final product thickness;
(b) roll bonding the layer to the strip to reduce their respective thicknesses by generally more than 50%;
(c) heating the layer and strip to a first selected temperature generally within a range of 1000°- 1300°F;
(d) maintaining the first temperature for a first selected time to promote metallic bonding of the layer to the strip while softening the base metal;
(e) pickling the layer and strip to remove surface oxides;
(f) roll bonding the layer to the strip to a thickness generally 11% greater than that of the desired final product thickness;
(g) heating the layer and strip to a second selected tem-perature generally within a range of 1250°-1400°F;
(h) maintaining the second temperature for a second selected time to effect dissolution of the beryllium into the copper and growth of metallic grains in the alloy to a desired size, with minimal diffusion of the base metal into the precious metal;
(i) pickling the strip and layer to remove surface oxides;
(j) roll bonding the layer to the strip generally to the desired final product thickness;
(k) heating the layer and strip to a third selected tem-perature generally within a range of 500°-800° F; and (l) maintaining the third temperature for a third selected time to resurrect strength, ductility and conductivity of the base metal.
21. The process set forth in claim 20 wherein step (b) comprises the step of cold rolling.
22. The process set forth in claim 20 wherein step (f) comprises the step of cold rolling.
23. The process set forth in claim 20 wherein step (j) comprises the step of cold rolling.
24. The process set forth in claim 20 wherein the precious metal comprises gold.
25. The process set forth in claim 20 wherein the precious metal comprises silver.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/114,651 US5370753A (en) | 1993-08-31 | 1993-08-31 | Process for cladding precious metals to precipitation hardenable materials |
| US114,651 | 1993-08-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2130290A1 true CA2130290A1 (en) | 1995-03-01 |
Family
ID=22356581
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002130290A Abandoned CA2130290A1 (en) | 1993-08-31 | 1994-08-17 | Process for cladding precious metals to precipitation hardenable materials |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US5370753A (en) |
| EP (1) | EP0640430B1 (en) |
| CA (1) | CA2130290A1 (en) |
| DE (1) | DE69410554D1 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6593010B2 (en) * | 2001-03-16 | 2003-07-15 | Hood & Co., Inc. | Composite metals and method of making |
| US20030096135A1 (en) * | 2001-11-20 | 2003-05-22 | Stern Leach Company, A Corporation Of The State Of Delaware | Composite jewelry metal |
| ITBO20020456A1 (en) * | 2002-07-16 | 2004-01-16 | Bomet S R L | BILAMINATE AND PE RLA METHOD MANUFACTURE WITH SUCH BILAMINATE |
| US6984358B2 (en) * | 2002-09-13 | 2006-01-10 | Lockheed Martin Corporation | Diffusion bonding process of two-phase metal alloys |
| CN100496970C (en) * | 2006-02-17 | 2009-06-10 | 贵研铂业股份有限公司 | Copper-base alloy composite material and its preparing method |
| CN100496971C (en) * | 2006-02-21 | 2009-06-10 | 贵研铂业股份有限公司 | Copper-base alloy composite material and its preparing method |
| US9655414B2 (en) | 2014-09-19 | 2017-05-23 | Leachgarner, Inc. | Age hardenable clad metal having silver fineness and a surface layer with enhanced resistance to tarnish, scratching, and wear |
Family Cites Families (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2608753A (en) * | 1947-05-24 | 1952-09-02 | Wilson H A Co | Clad beryllium-copper alloys |
| US2871150A (en) * | 1955-09-19 | 1959-01-27 | Westinghouse Electric Corp | Method of cladding molybdenum |
| US3302280A (en) * | 1964-05-15 | 1967-02-07 | Alloys Unltd Inc | Methods of bonding secondary materials to beryllium-copper |
| US3615902A (en) * | 1969-04-23 | 1971-10-26 | United States Steel Corp | Corrosion-resistant steel |
| US3959030A (en) * | 1974-12-30 | 1976-05-25 | Sumitomo Metal Industries, Ltd. | Method of producing aluminum coated steel |
| JPS53100931A (en) * | 1977-02-16 | 1978-09-02 | Mitsubishi Electric Corp | Plating pretreatment method for beryllium copper materials |
| US4354301A (en) * | 1979-09-13 | 1982-10-19 | Mitsubushi Kinzoku Kabushiki Kaisha | Method for manufacturing stripe-patterned metal plate |
| US4429022A (en) * | 1982-06-28 | 1984-01-31 | Olin Corporation | Composite material having improved bond strength |
| US4500028A (en) * | 1982-06-28 | 1985-02-19 | Olin Corporation | Method of forming a composite material having improved bond strength |
| US4565586A (en) * | 1984-06-22 | 1986-01-21 | Brush Wellman Inc. | Processing of copper alloys |
| US4599120A (en) * | 1985-02-25 | 1986-07-08 | Brush Wellman Inc. | Processing of copper alloys |
| JPS63257437A (en) * | 1987-04-10 | 1988-10-25 | Mabuchi Motor Co Ltd | Brush for small-sized motor |
| US5156923A (en) * | 1992-01-06 | 1992-10-20 | Texas Instruments Incorporated | Heat-transferring circuit substrate with limited thermal expansion and method for making |
-
1993
- 1993-08-31 US US08/114,651 patent/US5370753A/en not_active Expired - Fee Related
-
1994
- 1994-08-17 CA CA002130290A patent/CA2130290A1/en not_active Abandoned
- 1994-08-30 EP EP94306346A patent/EP0640430B1/en not_active Expired - Lifetime
- 1994-08-30 DE DE69410554T patent/DE69410554D1/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0640430A2 (en) | 1995-03-01 |
| EP0640430B1 (en) | 1998-05-27 |
| EP0640430A3 (en) | 1995-07-19 |
| US5370753A (en) | 1994-12-06 |
| DE69410554D1 (en) | 1998-07-02 |
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