Thermo-forming aluminium or magnesium alloy sheet - in which sheet is anodised before shaping by air pressure in heated die

摘要

The thin alloy blanks or sheet are coated, before forming with a layer (a) of artificial oxide, viz. Al2O3 or MgO, applied by a conventional process. Layer (a) is pref. 0.01 mu m thick, and is esp. 0.04-1 mu m thick; hot forming is pref. at 0.7-0.9 Tf, where Tf is the m.pt. of the alloy. Layer (a) is pref. obtd. continuously via electrolytic or chemical plant located upstream of the forming machine; or sheets already oxidised may be used. Layer (a) may be porous, anhydrous alumina obtd. electrolytically; or boehmite obtd. chemically. The hot pressed prods. can be directly coated with platics, varnish, paint, or other metal without any other surface prepn. Used in hot pressing, where a pressurised fluid forces the alloy sheet into a die, by the thermoforming process similar to that used in the plastic industry.