Investigating the corrosion behavior of as-cast Mg-Zn-Ca alloys with the same Zn/Ca atomic ratio by in situ observation

Abstract

The alloying contents with the same Zn/Ca atomic ratio of 0.13 on the corrosion behavior of Mg-Zn-Ca (ZX) alloys were investigated. The second phases in ZX10, ZX20, ZX30, and ZX51 alloys were identical with a majority of Mg₂Ca and very few Ca₂Mg₆Zn₃ and their distribution changed from isolated to continuous state in ZX30 and ZX51. ZX10 had the lowest corrosion rate of 0.55 mm/year after 168 h immersion in simulated body fluid solution due to the smallest number of sites of galvanic corrosion. The corrosion rate of ZX30 alloy was the highest (0.72 mm/year), while though ZX51 alloy had the most Mg₂Ca, its corrosion rate was reduced to 0.69 mm/year, resulting from the small size and thin Mg₂Ca. In situ microstructure observation demonstrated the high fraction Mg₂Ca phase and continuous Mg₂Ca with bulky size were the main reason for the fast corrosion rate.