US2586647A - Aluminum alloy - Google Patents

Description

Patented Feb. 19, 1952 UNITED STATE ALUMINUM ALLOY Harold Ernest Gresham, Little Eaton, and Douglas Wilson Hall, West Monkseaton, England, assignors to Rolls-Royce Limited, Derby, England No Drawing. Application February 4,1947, Se-

rial No. 726,440. In Great Britain February 8,

It is well known that artificially aged aluminium alloys when subjected to severe corrosion conditions such as salt water, mist or spray, are very prone to intercrystalline attack.

In order to avoid this corrosion effect high strength aluminium alloys such as Duralumin are coated with pure aluminium to give such materials as "Alclad.

Alloys are also used of aluminium with up to 3.5 per cent of magnesium and sometimes small additions of manganese. These alloys are of low strength but have high resistance to corrosion. They are however not susceptible to artificial age hardening unless other elements are added, and the elements hitherto added for this purpose have destroyed the corrosion resisting properties of the alloy.

We have found that the addition of silver 0.2 to 2% to an aluminium alloy containin 1 to 3.5% magnesium gives an alloy which responds to artificial ageing, moreover this alloy is equal to or more resistant to corrosion than the plain magnesium aluminium alloy. As a result of this artificial ageing the alloy is also stronger than the plain alloy.

The alloy preferably contains manganese and is of the following composition:

Per cent Magnesium 1 to 3.5 Silver 0.20 to 2.0 Manganese 0.05 to 1.0

Aluminium the remainder Other elements can be present in limited amounts.

Silicon which is an impurity in aluminium should not exceed 0.35 per cent and is preferably kept as low as possible.

Nickel can be present up to 2.0 per cent. Iron,

zinc, cobalt and zirconium may be present up to 1 per cent of each without seriously afiecting the alloy.

Antimony, tin, chromium, may be present up to 0.5 per cent of each.

Copper, titanium, beryllium, vanadium, molybdenum, tungsten, niobium, cerium and the rare earth elements may be used as cleaners and grain refiners upto a total of 1 per cent but with not more than 0.3 per cent of any individual element. For the rare earths Misch metal may be used and may be present up to 1.0 per cent. Other elements such as lithium, cadmium, calcium, strontium, barium, thorium, arsenic, lead, bismuth and others may be tolerated up to 0.1 per cent individually and 0.3 per cent total.

1 Claim. (01. 75-147) The preferred heattreatment is to give solution heat treatment at 520 to 550 C. for. 1 to 20 hours, to quench in Water and age at C. to 200 C. for 8 to 30 hours.

Aluminium the remainder was hot forged, solution heat treated at 550 C. for 2 hours quenched in water and aged for 24 hours at C. It gave a tensile strength of 18.5 tons per square inch with 22 per cent elongation. The rise in Brinell hardness which occurred as a result of the artificial agein was 40 points Brinell, i. e. it rose from 45 to 85 Brinell. Without the silver addition it would have remained at about 45 Brinell.

A well known widely used aluminium alloy containing 3.5 per cent magnesium, 0.5 per cent manganese, 0.25 per cent iron and 0.20 per cent silicon cast in the same mould and hot forged in the same manner was corrosion tested along with the new alloy.

The results before and after nine weeks intensive corrosion in sea water are as follows:

New Alloy Well-known Alloy Tensile Tensile Strength Elong' Strength Elong Tons Per Cent Tone Per Cent Before Corrosion 18.6 22 l7 18 After Corrosion 16.3 l7 l3 7. 5

Tensile strength Elongation Tom Per cent Before Corrosion 19.2 20 After Corrosion l7. 0 12 It will be observed this alloy is also superior to the well known alloy.

The alloy can be used either as castings or as forgings, being heat treated in either case to suit requirements. With forgings cold work may be introduced as a means of strengthening the alloy and may be carried out either after solution heat treatment and before ageing, or after the full heat treatment.

This alloy is also good for welding.

What we claim is:

An age hardened aluminum base alloy resistant to severe corrosion conditions and comprising an aluminum base alloy consisting of 94.5-98.8% aluminum, 1-3.5% magnesium and 0.20-2.0% silver in the condition produced by solution heat treatment of 1-20 hours at 520-550 (3., followed by quenching and 8-30 hours agein at 160-200" C.

HAROLD ERNEST GRESHAM. W

DOUGLAS WILSON HALL.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 1,920,090 Lyon et al. July 25, 1933 2,336,512 Stroup Dec. 14, 1943 2,388,540 Hartmann Nov. 6, 1945 FOREIGN PATENTS Number Country Date 432,964 Great Britain Aug. 2, 1935 132,612 Germany Apr. 5, 1901 OTHER REFERENCES "Practical Metallurgy, published by the American Society for Metals, 1940, page 32.

Age Hardening of Metals, published by the American Society for Metals, 1940, page 441.