US2726436A - Metal-clad aluminum alloys - Google Patents

Description

United States Patent METAL-GLAD ALUMINUM ALLOYS Frederick Alfred Champion, Beaconsfield, England, as signor to The British Aluminium Company Limited, London, England, a company of Great Britain No Drawing. Application August 7, 1951, Serial No. 240,789

Claims priority, application Great Britain October 31, 1950 1 Claim. (Cl. 29--197.5)

This invention relates to composite metals which are composed of two or more tenaciously adhering layers each containing aluminium as the major constituent, the metal of each layer being referred to herein as an aluminium-base metal. One of these layers referred to herein as the core, may be formed from an alloy chosen to provide certain characteristics, such as high mechanical strength, While the other or others, which cover the core on one or both sides and are termed herein cladding, are of substantially pure aluminium or of an alloy selected for its high resistance to corrosion and the fact that it is more electro-negative than the alloy of the core, so that the cladding will provide sacrificial protection to the core if the latter becomes locally exposed by damage to the cladding.

For example, aluminium alloys of high strength but relatively low corrosion resistance have been used for the core and covered with cladding of higher corrosion resistance such as aluminium of 99.7% purity. It is also known to apply cladding to a core composed of an aluminium-1%% manganese alloy which itself has a good corrosion resistance, the cladding being composed of an aluminium alloy containing zinc or one or more of those metals which when alloyed with aluminium will yield a product having the required sacrificial protective action. The metal-clad alloy has a greater resistance to pitting or local corrosion than either the core or the cladding when exposed separately to the corrosive influence.

The metal-clad aluminium alloys so far known to us sulfer from the defect that they are liable to become discoloured or stained when they come into contact with certain natural waters although they may be resistant to serious corrosion.

Now it is well-known that aluminium of very high purity, which will be referred to herein as super purity aluminium and is defined as containing at least 99.95% of aluminium, is particularly resistant to corrosion and discoloration. It is also known that substantially pure aluminium of lower purity than super-purity aluminium and aluminium alloys containing manganese, magnesium, or both, are themselves relatively resistant to corrosion, examples of such alloys being those containing l%% manganese, 2 A% magnesium+ /z% manganese, or 1% manganese+I% magnesium. However, if super purity 2,726,436 latented Dec. 13, 1955 aluminium is used as a cladding on a core of substantially pure aluminium or of such an aluminium alloy having an intrinsically high corrosion resistance there is not a sufiicient difference in solution potential between the core and cladding to ensure the necessary sacrificial protection, and in the event of damage to the cladding, pitting will not be prevented.

We have now found that the necessary difference in solution potential between a cladding of super purity aluminium and a core of highly corrosion resistant aluminium-base metal of the kind mentioned above, may be ensured by making a controlled addition of copper to the core metal without materially reducing the natural corrosion resistance of the core. In this way it is possible to produce composite aluminium-base metals which are suitable for the manufacture of articles required to withstand corrosion and to maintain a bright and pleasing appearance, such as trays for domestic use, cooking utensils and kettles.

Accordingly, the present invention consists in a composite aluminium-base metal composed of a core of corrosion resisting aluminium or aluminium alloy, e. g. an alloy containing 1%% manganese, 2% magnesium+ /z% manganese, or 1% manganese+I% magnesium, and a cladding of super purity aluminium, wherein the core metal contains from 0.10 to 0.30%

copper.

The cladding may be on one or both sides of the core. When the core is composed of aluminium-1%% manganese alloy the copper content of the latter is preferably between 0.10 and 0.20%. When magnesium is present in the core metal slightly more copper may be advantageous.

A composite material in accordance with this invention is particularly suitable where high resistance to staining and corrosion is required and where high mechanical strength is not necessary but the strength of super purity aluminium alone would be inadequate, for example, in the manufacture of hollow-Ware.

I claim:

A composite aluminium-base metal composed of a core of an aluminium alloy consisting of aluminium plus 1%% manganese and from 0.10 to 0.20% copper and a cladding on at least one face composed of aluminium of at least 99.95% purity.

References Cited in the file of this patent UNITED STATES PATENTS 1,865,089 Dix June 28, 1932 1,873,470 Peek Aug. 23, 1932 1,997,165 Brown Apr. 9, 1935 1,997,166 Brown Apr. 9, 1935 2,084,327 Edwards June 22, 1937 2,100,411 Reuleaux Nov. 30, 1937 2,240,732 Wood May 6, 1941 2,312,039 Hoglund Feb. 23, 1943 2,376,681 Gauthier May 22, 1945 2,586,647 Gresham Feb. 19, 1952