Elucidating the dependence of corrosion behavior and mechanical property on the grain structure of low-temperature as-extruded Mg–Zn–Ca–Zr alloy

In this work, the synergistic influences of grains structure, precipitate phase particles and crystal orientation on corrosion mechanism of low-temperature as-extruded Mg–4.6Zn–0.3Ca–0.4Zr (wt%) alloys were systemically studied in SBF bio-corrosion solution. Microscopic indicated that the as-extruded specimens shown a typical bimodal micro-morphology comprising of elongated undynamic recrystallization (un-DRX) grains and fine DRX grains, accompanying by a small amount of randomly distributed Mg₇Zn₃ particles. Analysis of corrosion mechanism demonstrated that the Mg₇Zn₃ particles, grain boundaries and basal grains were more cathodic than α-Mg matrix, viz. 0.081 V, 0.042 V and 0.017 V, respectively, and served as cathode sites during immersion to promote micro-galvanic corrosion occurrence of adjacent grains and formation of insoluble corrosion products layer. The corrosion products layer were mainly composed of Mg(OH)₂/MgO, Ca₃(PO₄)₂, Mg₃(PO₄)₂, and Ca₁₀(PO₄)₆(OH)₂ (HA_p). Hence, the superior corrosion resistance of as-extruded specimen was mainly attributed to multiple factors including grain refinement, weak second-phase interaction, mixed corrosion products and basal texture advantage.