Clarification of the necessary value of surface roughness for developing luster on an AZ31 magnesium alloy surface with or without acid aqueous solution treatment

Abstract

To shorten the press forming and surface treatment process for AZ31 magnesium alloy by eliminating the need for mechanical polishing of the press-formed surface, we determined the necessary value of surface roughness, Ra, for developing a luster on surface with or without acid aqueous solution treatment. The target value for the gloss of AZ31 magnesium alloys was set to be that of the surface after mechanical polishing by using emery paper #2000. To achieve this gloss solely by mechanical polishing without acid aqueous solution treatment, the surface roughness, Ra, had to be less than 0.2μm. If the acid aqueous solution treatment was applied to the mechanically polished surface, the necessary surface roughness, Ra, before the treatment was 1.5 μm. The increase in gloss as a result of acid aqueous solution treatment results from smoothing of small surface convexo-concave features measuring less than 0.2μm. Because the surface roughness, Ra, of articles press-formed by using 100,000 times square-cup drawings was 0.3μm, the mechanical polishing stage could be eliminated from the process for developing a luster, and the acid aqueous solution treatment could be applied directly. © 2008 The Japan Institute of Metals.