Patent ID: 8608869
Filing Date: 2013-12-17
Classification: C23C,C23F,C25D

Abstract:
1. A method of improving the corrosion resistance of a cast article formed by solidification of a magnesium alloy with an overall composition comprising at least 85 percent by weight of magnesium and at least about 5 percent by weight of aluminum, the cast article having an as-cast surface and a microstructure comprising grains with a grain size, the grains being magnesium rich and having a magnesium content greater than the overall alloy magnesium content, the grains being separated by a near-continuous layer of grain boundary material, generally enclosing the grains, the material having an aluminum content greater than the overall alloy aluminum content, the method comprising: treating the surface of the article with an aqueous solution comprising a salt, the aqueous salt solution being suitable for preferential reaction with the magnesium-rich grains of the article surface to form removable magnesium-containing reaction products extending inwardly from the as-cast article surface to a reaction depth of between 1 and 5 times the grain size; and removing the magnesium-containing reaction products to expose cavities from removed magnesium material, the cavities being bounded with residual aluminum-enriched grain boundary material.