US 2966734 A
Description (OCR text may contain errors)
2,966,734 ALUMINUM BASE ALLOY POWDER PRODUCT Raymond J. Towner and John P. Lyle, Jr., New Kensington, Pa., assignors to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Filed Mar. 27, 1958, Ser. No. 724,230
3 Claims. (Cl. 29-182) This invention relates to articles made from aluminum States Patent G base alloy powders and it is more particularly concerned ,coated aluminum flake powders have been produced which possess unique strength properties at elevated temperatures. The particles of oxide distributed throughout the body appear to impart the unusual strength at elevated temperatures. The production of the oxide-coated flakes is time consuming and consequently expensive. It has now been found, contrary to previous belief, that useful articles can be made from certain types of atomized alu minum alloy powders. As is well known, the atomization process involves disintegrating a stream of molten metal with a jet of gas, such as compressed air, or by mechanical means. Very finely divided particles can be produced by this process that will pass through a standard Tyler 100 mesh screen.
It is an object of this invention to provide articles having a high strength at elevated temperatures which are made from atomized particles of an aluminum base alloy containing tungsten as the principal added alloy component.
Another object is to provide such articles which do not require any preliminary thermal treatment to place them in condition for service at elevated temperatures.
Still another object is to provide an article made from atomized aluminum-tungsten alloy powder that does not depend upon the presence of oxide particles to impart strength at elevated temperatures.
These and other objects are achieved by atomizing a substantially iron-free aluminum base alloy containing not less than 70% by weight of aluminum and 1 to 15% by Weight of tungsten as the principal added alloy component, ,and subsequently consolidating and working a mass of such atomized particles under the influence of heat and pressure. The resultant articles have a density closely approximating that of the alloy if cast; and in the hot worked condition, they have a tensile strength of not less than 10,000 p.s.i. and a minimum yield strength of 9,000 p.s.i. at 600 F. after a 100-hour exposure. These tensile and yield strength values are to be compared with those of some conventional wrought heat treated aluminum base alloys that have been recommended for service at elevated temperatures. For example, a wrought aluminum base alloy nominally composed of aluminum, 12.2% silicon, 1.1% magnesium, 0.9% nickel and 0.9% copper has in the solution heat treated and age hardened condition a tensile strength of only 5,000 p.s.i. and a yield strength of 3,000 p.s.i. after exposure at 600 F. for 100 hours. Under the same exposure conditions, a second well-known aluminum base alloy nominally consisting of aluminum, 4.5% copper, 1.5% magnesium and 0.6% manganese, when worked, solution heat treated and age hardened, has a tensile strength of 10,000 p.s.i. and a yield strength of 7,500 p.s.i.
2,965,734 Patented Jan. 3, 1961 ice The aluminum-tungsten powder products can be readily worked under the usual hot working conditions of temperature and pressure employed in fabricating conventional aluminum and aluminum base alloy articles. Furthermore, the hot-worked product can be cold worked to a limited extent, desired. The fabricated aluminum alloy products can be placed in service without any preliminary thermal treatment. The strength of the wrought powder products at elevated temperatures is not influenced to any significant extent by the oxide film which coats the atomized particles.
The atomized alloy particles are preferably prepared by melting the alloy of the desired composition and projecting it through a suitably designed nozzle with the aid of a compressed gas. The atomizing conditions should be so adjusted that none or only a small proportion of the particles are larger than mesh microns opening) and that the majority of the particles will pass through a 200 mesh screen (74 microns opening). The particles produced in this manner generally have an irregular shape but for the most part are substantially equiaxed in dimensions and have as-cast structure. The aluminum-tungsten constituent in the alloy is very finely divided as a result of the drastic chill associated with the atomization process. The surface of the particles are, of course, oxidized if the atomization has occurred in air or in some other oxidizing atmosphere, however, the oxide skin is very thin and the amount of oxide introduced into the final product is too small to affect the properties thereof to any significant extent.
The tungsten content of the alloy should be between 1 and 15% by weight, as mentioned above, and preferably within the range of 5 to 10% to obtain the highest strength at elevated temperatures. If less than 1% is employed, the minimum strength is not achieved and if more than 15% is present, the worked article has insuflicient ductility and may fracture under applied stresses. Tungsten is substantially insoluble in aluminum and whatever small proportion may be dissolved is too small to have any significant effect upon the properties of the atomized particles. It will therefore be appreciated that the matrix of the atomized particles consists of aluminum with a dispersion of finely divided aluminum-tungsten constituent distributed throughout the particle. The high strength at elevated temperatures appears to be controlled by the amount of the aluminumtungsten constituent and the fineness of the dispersion.
The alloy may contain the usual impurities associated with aluminum, for example, silicon and iron. Generally, the silicon impurity should not exceed 0.8% and the iron content should not be more than about 1% Other impurities, such as copper, may be present in amounts up to 0.5%. In view of the relatively small amount of iron impurity permitted in the alloy, the composition is referred to herein as being substantially iron-free.
For some purposes, it may be desirable to add one or more elements selected from the group composed of nickel, cobalt, manganese, chromium, titanium, vanadium, zirconium and molybdenum in amounts of 0.1 to 10% each, the total not exceeding 10%. These elements act as hardeners and, like tungsten, are substantially insoluble in the aluminum matrix. To attain the properties attributable to the aluminum-tungsten constituent, the tungsten content of the alloy should exceed the total amount of any added hardener elements.
To make the wrought article from the atomized powder, the powder may be initially formed into a compact that is subsequently worked or it may be charged directly to a compression chamber such as an extrusion press cylinder and be extruded therefrom after initial consolidation of the mass. The initial compact may be made by heating the powder to a temperature between 700 and 3 900 F. and applying a sufficient pressure thereto for a long enough period of time to cause at least some consolidation and welding of the atomized particles. Pressures of 200 ;to 150,000 p.s.i. are satisfactorywhich are a t ea nt s m a mo m eratu e and when a 600 F. after a 100-hour exposure at that temperature. The composition of the alloy tested and the tensile properties at both room temperature and at 600 F. are given less to a few hours. Generally, a longer time isrequired [where low pressures are" employed. Thecompact may be left in the press cylinder and then' extruded, or it may be'ejec'ted, cooledfscalped, reheated to the hot working temperature and hot worked. In some cases it may be desirable to reheat the compact to temperatures as high as 1150 F. before hot working in order to obtain adequate workability. This should only be done if more than 3% tungsten is present. Where the powder is charged to a compression chamber, it may be initially heated to a temperature between 700 and 900 F. and introduced tothe chamber or it may be charged cold and heated within the chamber. Alternatively, it may be heated to an intermediate temperature, then charged to thechamber and brought to the desired temperature. When the powder is to be compacted and immediately extruded, it is generally convenient to compress the pewdered mass againsta blind die in a press cylinder and then substitute an extrusion die for it to produce the desired extruded shape. Although reference has been made to the extrusion of the powder mass, it is' to be understood that it can be subjected to other types of hot working operations, such as rolling, forging or pressing, providing a suitable compact is initially produced. The hot working is preferably performed within the temperature range of 700 to 900 F.
Our invention is illustrated by the following example wherein an aluminum-tungsten atomized powder was conlsolidatedand the product hot worked. The powder was of a fineness such that approxim ately'7S% passed through a 200 mesh screen and substantially all of the remainder passed through a 100 mesh screen. "The alloy powder was charged to an extrusion press cylinder preheated to 800 F. and compressed against a blind die under a pressure of 100,000 p.s.i. for a period of approximately one minute. In the course of charging and compressing the powder the temperature of the'eompact reached 700- 800 F. After the compact'was thus formed it was ejected from the cylinder, cooled to room temperature, scalped, reheated to 800 F., inserted in an extrusion cylinder heated to 80051 and extruded into the form of a rod in diameter. Tensile specimens were cut from the extruded rod and tested without any preliminary therapplied for varying periods of time from a minute or 5 in Table 1 below.
TABLE 1 Tensile properties of extruded Al-W powder product At Ro omTemperature At 600 F.
Alloy Percent W Tensile Yield Percent Tensile Yield Percent Strength, Strength, Elong. Strength, Strength, Elong. p.s.i. p.s.i. p.s.1. p'.s.l.
It isapparent from the foregoing that the tensile and yield strengths of the alloy are higher than those of the two commercial aluminum base alloys referred to hereina b ove." It is also significant that the high strength at '600 F. was obtained'without any preliminary thermal worked powder article being formed from atomized powder from an aluminum base alloy containing at least by weight of aluminum and from 1 to 15% of tungsten as the essential component, the amount'of said component exceeding the total quantity of any hardening elements present in the alloy, said alloy being substantially free from elements which form a solid solution with aluminum, except as they occur as impurities, said hot worked article being characterized in the as-worked condition by a tensile strength at 600 F. after a hour exposure of not less than 10,000 p.s.i. and a yield strength of not less than 9,000 p.s.i.
2. A hot worked aluminum base alloy powder article according to claim 1 wherein the tungsten content is 5 to 10%.
3. A hot worked aluminum base alloy powder article according to claim 1 wherein the alloy also contains at least one hardening element selected from the group consisting of nickel, cobalt, manganese, chromium, tita nium, vanadium, zirconium and molybdenum in amounts of 0.1 to 10% each by weight, the total not exceeding 10% by weight, the tungsten content ofsaid alloy exceeding the total amount of hardening elements added thereto. Y e
References .Cited inthe file of this patent UNITED STATES PATENTS 2,188,203 Mansfield Jan. 23, 1940 2,287,251 Jones June 23, 1942 2,809,891 .Ennor Oct. 15, 1957