ZINC-DIFFUSED LAYER FOR CORROSION PREVENTION OF ALUMINUM

摘要

PURPOSE:To improve the pitting corrosion resistance of an Al alloy by specifying the surface concn. of zinc and depth of a zinc-diffused layer. CONSTITUTION:The surface concn. of zinc of the zinc-diffused layer is specified to <=12% and the depth of the zinc-diffused layer to <=200mu. The surface concn. (%) of zinc X depth (mu) of the zinc-diffused layer is specified to (mu) >= 400. The pitting corrosion resistance of the Al alloy is remarkably improved by the sacrificial anode effect of the zinc-diffused layer and the corrosion-resistant life of apparatus parts made of the Al alloy is remarkably improved if such zinc-diffused layer is provided to the surface layer of the Al alloy. The corrosive wear of the zinc-diffused layer is significant on the contrary if the surface concn. of zinc is >=12%. The ratio of the zinc-diffused layer is too high with respect to the thickness of the parts and the pitting-resistant life is no longer improved if the depth of the zinc-diffused layer is >=200mu. The product of the surface concn. of zinc and the depth of the zinc-diffused layer is required to be >=400 from the pitting depth of a wetting test with an aq. copper chloride soln. and salt-contg. mud.