Magnesium alloys containing magnesium and various additive elements have been used for constituent materials for various structural members such as housings for portable electric/electronic devices including cellular phones and laptop computers and parts of automobiles.
For structural members made of magnesium alloys, a cast material (an AZ91 alloy specified in American Society for Testing and Materials (ASTM) standards) produced by a die casting process or a thixomolding process is in the mainstream. In recent years, structural members obtained by press-forming sheets made of wrought magnesium alloys represented by an AZ31 alloy specified in the ASTM standards have been being used. Patent Literature 1 proposes a magnesium alloy sheet which is made of an alloy corresponding to the AZ91 alloy specified in the ASTM standards and which is excellent in press formability.
Since magnesium is an active metal, surfaces of the structural members and magnesium alloy sheets used to manufacture the structural members are usually subjected to anticorrosion treatment including anodic oxidation treatment and chemical conversion treatment.