Effects of Ca addition on microstructure, mechanical properties and corrosion behaviors of solution treated Mg-5Ga-xCa alloys

Abstract

Effects of Ca addition on microstructure, mechanical properties and corrosion behaviors of solution treated Mg-5Ga-xCa (x = 0, 0.2, 0.5, 0.8 wt%) alloys are investigated. The Mg5Ga2 phase is almost dissolved into the matrix after solution treatment, while the residual phases mainly the Mg-Ga-Ca phase increases with the higher Ca content. The solution treated Mg-5Ga-0.2Ca alloy exhibits the highest corrosion resistance (with the average weight loss rate of 0.349 mg·cm−2·d−1 in Hank’s solution for 7 days) and the appropriate mechanical properties, with the ultimate tensile strength of 212 MPa and the elongation to rupture of 16.9%. Its high corrosion resistance can be mainly attributed to the protective effect of the Mg2Ca phase as a corrosion anode with low standard potential, the well-protected corrosion product film and the small grain size, while its good mechanical properties are due to the grain refinement and the solid solution strengthening of more Ga atoms. With a further increase in Ca content (≥0.5 wt%), although the grains are more refined, both the mechanical properties and corrosion resistance of the alloy decrease because of the residual phases in large quantities and low solution of Ga atoms.