THERMALLY TREATED METALLIC COATED FERROUS BASE PRODUCT HAVING IMPROVED CORROSION RESISTANCE AND METHOD OF MAKING PRODUCT

摘要

This invention relates to an aluminum-zinc alloy coated ferrous base product which exhibits improved atmospheric corrosion resistance, and to the process whereby such improved corrosion resistance may be realized. The process is characterized by the steps of heating such coated product to a temperature within the single phase region for the composition corresponding to the aluminum and zinc of said coating, defined as alpha in the FIGURE in the accompanying drawing, preferably at a temperature between about 650 DEG F. (343 DEG C.) to 750 DEG F. (399 DEG C.), for a period of time to solution treat the aluminum-zinc alloy coating overlay, and cooling slowly to at least 350 DEG F. (177 DEG C.). The resulting product is characterized by improved atmospheric corrosion resistance as a result of the combination of an aluminum-zinc alloy coating overlay having a structure comprised of a fine dispersion of beta-zinc within a matrix of alpha-aluminum, and a thin intermetallic layer interposed between said overlay and said ferrous base.