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
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/057—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with copper as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/12—Alloys based on aluminium with copper as the next major constituent
• • 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

Definitions

• This invention relates to improving the tensile strength and resistance to corrosion of articles of certain thermally treated aluminum base alloys and it is particularly concerned with the interposition of a cold working step before the final thermal treatment of the articles.
• Aluminum base alloys composed essentially of aluminum and 4 to 7% by weight of copper and free from magnesium do not follow the pattern of those alloys referred to hereinabove in the response to the precipitation treatment and the increase in strength attained by that treatment where cold working precedes precipitation. Furthermore, this difference in response adversely affects the resistance to corrosion in the absence of cold work. As a consequence, alloys of this type have enjoyed but limited use although they possess advantageous properties in other respects than strength at room temperature and resistance to corrosion.
• My invention is directed .to improving the strength and resistance to corrosion of articles of precipitation hardened aluminum-copper alloys of the foregoing type Patented May 31, 1956 ice and has as its primary object the provision of a method for treating articles of such alloys. It is also an object of this invention to provide a method of treating a wrought article or a portion thereof composed of an essentially binary aluminum-copper alloy whereby a higher strength and a better resistance to corrosion is developed than in the same alloy which has not received any cold work before the precipitation hardening treatment.
• the type of alloy which is improved by my process is one that is composed essentially of aluminum and from 4 to 7% by 'Weight of copper and free from magnesium and zinc except as they occur as impurities.
• the alloy should contain at least 4% copper in order to attain a high strength while on the other hand more than 7% introduces problems in working the alloy and the increased copper content does not produce a significant increase in strength. when the alloy is cold Worked and precipitation hardened. Other elements which are substantially insoluble in solid aluminum may be present in relatively small amounts.
• At least one of the group of hardening elements consisting of manganese, titanium, vanadium, zirconium, molybdenum, tungsten, chromium, boron, nickel, cobalt, tantalum and niobium can be present in the following amounts: 0.15 to 1.2% manganese, 0.05 to 0.20% vanadium, 0.05 .to 0.30% zirconium, and 0.1 to 0.25% each of titanium, molybdenum, tungsten, chromium, boron, nickel, cobalt, tantalum and niobium. The total amount of these elements with. the exception of manganese, vanadium and zirconium, should not exceed about 0.25%.
• At least one of the group of low melting point elements consisting of lead and bismuth may be added in amounts of 0.1 to 0.75% each, the total not exceeding 1.5%.
• the foregoing elements adversely affect the physical properties of the alloy, and being substantially insoluble in solid aluminum they do not interfere with the solution and precipitation of the copper.
• the alloys are substantially free from elements such as magnesium and zinc which are soluble in solid aluminum, except as they may occur as impurities.
• the magnesium impurity content should not exceed 0.02% and the zinc content should not be over 0.25%
• the first step in my process consists of a solution heat treatment which consists of heating the alloy to a temperature between 900 and 1050 F. and holding within this range for a period of time, on the order of A to 12 hours, to effect substantially complete solution of the copper.
• the alloy is to be quickly cooled to much lower temperature, generally room temperature or one not far removed from room temperature.
• the chilling may be accomplished in any one of several conventional ways as by quenching in water, or by a water spray or even an air blast, if the article is not too thick.
• the alloy article Upon attaining room temperature or close to it, the alloy article is strain hardened either by a reduction in cross section by rolling, pressing, drawing or by other known metal working methods or simply by flattening or stretching the article, for example, the work which is done in straightening a warped product.
• the amount of cold work that can be employed depends upon the nature of the article and the ease of making reductions, thus, only a relatively small reduction can be made on extrusions and tubing by stretching, but sheet can be reduced by a much larger amount. Generally from 1 to cold work is preferred since most of the advantages are obtained within this range and because in some cases, the size of the product precludes greater amounts of cold work.
• the alloys to which the above-described treatment is applied should be in the wrought condition, as distinguished from castings.
• the wrought forms may be produced by any of the conventional methods such as by rolling, forging, extrusion, pressing, and the like. In many instances these are performed at elevated temperatures and hence are referred to as hot working operations as distinguished from those performed at room temperature.
• the welded structure is solution heat treated, quenched, the welded area cold worked and finally precipitation hardened. In this manner the weld bead and worked area adjoining it are improved.
• the calculated length of time represents the minimum that should be used in practice. Exceeding this period by two hours, for example, has but a slight effect on the yield strength, generally less than 3,000 psi. The resistance to corrosion of a product which has been so treated is adequate for many applications.
• the minimum period of precipitation hardening should be determined in accordance with the following equation: 55
• Example 1 An alloy nominally composed of aluminum, 6.5% copper, 0.25% manganese, 0.1% vanadium, 0.15% zirconium 40 and 0.05% titanium was melted, cast into ingot form, hot
• Samples of the sheets were also exposed to standardized corrosion tests wherein some of the samples were placed under a stress equivalent to 75% of the yield strength while other samples were not subjected to any stress. Both stressed and unstressed samples were alternately immersed and raised from an aqueous solution of 3.5% NaCl over a period of 12 weeks. At the conclusion of the 12 week period the samples were subjected to a tensile test and the loss in strength as compared to that of samples of the original material was noted. The percentage loss in strength of the specimens is given in Table II below.
• Example 2 The benefit of cold working another type aluminumcopper alloy is illustrated in the case of an alloy nominally composed of aluminum, 5.5% copper, 0.5% lead and 0.5% bismuth. An ingot of this alloy was hot rolled to rod form 2 inches in diameter. Sections were cut from the rod, solution heat treated at 975 F. for 2 /2 hours and quenched in cold water. One group (D) was heated to 320 F. and held for 14 hours while the second group (B) was cold drawn with a reduction in cross section of 20% before beingheated to 320 F. and held at that temperature for 14 hours which is close to the time determined according to Equation 2. The average tensile properties of the samples taken in a longitudinal direction are given in Table III below.
• the alloy also contains at least one of the group of hardening elements composed of 0.15 to 1.5% manganese, 0.05 to 0.20% vanadium, 0.05 to 0.3% zirconium, and 0.01 to 0.25% of titanium molybdenum, tungsten, chromium, boron, nickel, cobalt, tantalum and niobium, the total amount of said elements except for manganese, vanadium and zirconium not exceeding 0.25
• the alloy also contains at least one of the low melting point elements of the group composed of lead and bismuth in amounts of 0.1 to 0.75% each, the total not exceeding 1.5%.
• the method of improving both the yield strength and resistance to corrosion of welded articles in the welded area wherein the filler metal is composed of an alloy consisting essentially of aluminum and 4 to 7% by weight of copper, and free from magnesium and zinc except as impurities comprising heating said filler metal in said welded area to a temperature between 900 and 1050 F. or a period of A1 to 12 hours, quenching said heated filler metal, cold working the filler metal and the area immediately adjacent thereto from 1 to 20% and thereafter heating said cold worked metal to a temperature between 300 and 400 F. for a period of 1 to 48 hours to induce precipitation hardening, and for a minimum length of time needed to develop a maximum yield strength, said time being determined from the equation:

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• Crystallography & Structural Chemistry (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
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• Conductive Materials (AREA)

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Citations (5)

• 1963
  • 1963-09-11 US US308085A patent/US3253965A/en not_active Expired - Lifetime
• 1964
  • 1964-09-09 NL NL6410481A patent/NL6410481A/xx unknown
  • 1964-09-10 DE DEA47044A patent/DE1300302B/de active Pending
  • 1964-09-10 BE BE652897D patent/BE652897A/xx unknown
  • 1964-09-10 GB GB37172/64A patent/GB1023674A/en not_active Expired

Patent Citations (5)

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