US2372546A - Zinc base alloy - Google Patents

Description

Patented Mar. 27, 1945 UNITED STATES PATENT OFFICE ZINC BASE ALLOY 4 Edward 8. Bdrm, Rome,'N.

Copper and Brass Inco a corporation of Maryland N Drawing. Application September 9, 1943, Serial No. 501,670

4 Claims.

. contain 0.4 to 5% copper, 0.05 to 0.75% alumi-.

num, and 0.05 to 0.75% substance of the group consisting of arsenic and phosphorus.

Applicant has found that the tensile strength and resistance to shock or impact loading of zinc can be much increased, without an unsatisfactory decrease in its ductility for many uses, by adding to it small amounts of copper aluminum and substance of the above mentioned group. At the same time the tensile strength, shock resistance and ductility will be maintained at a markedly higher value when the allow is annealed or when it ages, making the alloy suitable for uses for which zinc is wholly unsuited.

For example, zinc in the hot rolled condition has a tensile strength of about 17,000 pounds per square inch, a Charpy impact resistance of about 48 foot pounds per square inch, and a ductility corresponding to an elongation of. about 45% in 2 inches, but when the hot rolled metal is annealed at 600 F. for 1 hour has a tensile strength of about 6,000 pounds per square inch, a Charpy impact resistance of about 32 foot pounds per square inch, and an elongation of only 4% in 2 inches, and when the annealed alloy is subjected to moist steam at 95 C. for days, which is the standard accepted test for determining the effect of age on zinc and its alloys, has approximately the same tensile strength and Charpy impact resistance as when so annealed, but with the meager elongation of only 2% in 2 inches. The improved alloy, on the other hand, when hot rolled has a tensile strength of from 40,000 to 60,000 pounds per square inch as compared to 17,000 for zinc, and an elongation of from 20 to 45% in 2 inches, depending upon the exact amounts of its several constituents. When subjected to the same annealing mentioned above, the improved hot rolled alloy has a tensile strength of .from 31,000 to 55,000 pounds per square inch as compared to 6.000 for zinc, a Charpy impact resistance of 126 to 395 as compared to 32 for zinc, and an elongation of from 20 to 35% in 2 inches as compared to 4% for zinc. When the improved annealed lot rolled alloy is subjected to the steam test it has a tensile strength of from,27,000 to 52.000 pounds per square inch as compared to 6,000 for zinc, a Charpy impact resistance of 80 to 309 as compared to 32 for zinc, and an elongation of from 16 to 37% in 2 inches as compared to 2% for zinc.

Zinc further has the defect of self annealing when cold worked by usual mill processes, mak- Y., asslgnor to Revere rporated, Rome, N. Y.,

ing it difilcultunder such conditions to harden it by cold working. The improved alloy, on the other hand, does not have this defect if the amount of copper contained therein is about 1.5% or more, and with such percentages of copper can readily be given controlled degrees of hardness by controlled amounts of cold working.

The improved alloy has excellent hot plasticity,

enabling it to be not worked by rolling, extrusion, forging, etc., say hot rolled into sheets. It also can be commercially cold worked, say cold rolled into sheets, best results in this respect being secured when the amount of copper is approximately 1.5% or more, or, ii the copper is below 1.5%, when the amount of substance of the group mentioned does not exceed approximately of the amount of aluminum.

The great decrease in the strength and ductility of zinc occurring when it is annealed or aged arises because of a coarsening of its crystalline structure, this phenomena commonly being termed "grain growth." Alloys resulting from attempts to cure grain growth or eliminate its effects by adding small amounts of other elements to zinc commonly are subject to intergranular corrosion and alloy phase changes, the latter causing the zinc to be dimensionally unstable, both coupled with poor workabilit and unsatisfactory ductility and unsatisfactory stability with age in respect to ductility. For example, when copper and aluminum within the ranges thereof in the improved alloy are added to zinc without adding substance of the group mentioned the resulting ternary alloy, although having a high tensile strength, is seriously subject to intercrystalline corrosion and dimensional instability coupled with such poor ductility and mechanical workability that it is practically Worthless except for die castings. The improved alloy however is satisfactorily resistant to intercrystalline corrosion and exhibits no change in dimensions as it ages, besides being, as above pointed out, hot and cold workable and possessing satisfactory ductility and stability in the latter respect for most uses.

The above mentioned properties of the improved alloy will be secured if the sum of the amounts of aluminum and substance of the group mentioned present in the alloy does not exceed approximately the amount of copper present. Otherwise assurance will not be had against intercrystalline corrosion or that the alloy will be dimensionally stable. Commonly best results in respect to securing good all around properties in the improved alloy will be secured stability of the ductility when the alloy is annealed or ages commonly will be had when the amount of substance oi. said group is at least the amount of aluminum.

Further, to secure best results in respect to intercrystalline corrosion and resistance to corrosive media, it is desirable to employ, in the improved alloy, commercial zinc of fairly high purity as, for example, that termed High Grade No. 1 in A. S. T. M. specification B6-37, which latter grade contains a maximum of 0.07% each of lead and cadmium impurities and a maximum of 0.02% iron impurity, the total of such of these impurities as may be present not exceeding 0.1%, and is substantially free from all other impurities. Although the same mechanical properties will be secured in the improved alloy with poorer commercial grades of zinc, no assurance will be had that it will not be more or less subject to corrosion in both respects mentioned and will not be more or less dimensionally unstable as it ages.

The excellent properties of the improved alloy are exhibited by the following table, in which the steam test referred to is that above mentioned:

Hot rolled,

Hot rolled, annealed at Percentages As hot rolled 2% an}??? g g fgg for 1 hr. subjected to steam test Cu Al As '1 0 0 17 45 6 4 6 2 l 0. 0. 75 40 20 31 20 27 20 l 0. 5 0. l 42 33 37 24 32 16 5 O. 05 0. 75 63 29 46 31 45 30 5 0. 6 0. 1 57 38 55 21 49 17 T tensile strength in 1.000 glounds per square inch. E per cent elongation in 2 ches.

It will be understood that, within the scope of the appended claims, iurther constituents may be added for modifying the properties of the improved alloy or for securing additional properties, so long as the characteristics imparted to the zinc by the addition of copper, aluminum and substance of the group consisting of arsenic and phosphorus are not substantially destroyed.

I claim:

1. Zinc base alloys having, approximately, 0.4 to 5% copper, 0.05 to 0.75% aluminum, and 0.05 to 0.75% substance of the group consisting of arsenic and phosphorus, the sum of the percentage amounts of aluminum and said substance not exceeding the percentage amount of copper, the balance being substantially zinc.

2. Zinc base alloys having, approximately, 0.4 to 5% copper, 0.05 to 0.75% aluminum, and 0.05 to 0.75% substance of the group consisting of arsenic and phosphorus, the percentage amount of said substance not exceeding of the percentage amount of aluminum when the percentage amount of copper does not exceed 1.5%, the sum of the percentage amounts of aluminum and said substance not exceeding the percentage amount or copper, the balance being substantially zinc.

3. Zinc base alloys having, approximately, 0.7 to 4.5% copper, 0.4: to 0.65% aluminum, and 0.05 to 0.5% substance of the group consisting of arsenic and phosphorus, the percentage amount of said substance not exceeding approximately 80% of the percentage amount of aluminum, the sum of the percentage amounts of aluminum and said substance not exceeding the percentage amount of copper, the balance being substantially zinc.

4. The alloys according to claim 1 in which the percentage amount of substance of the group specified is at least the percentage amount of aluminum.

EDWARD S. BUNN.