Microstructure and enhanced corrosion resistance of biodegradable Mg–Gd–Cu–Zr alloy by solution treatment

Abstract

Mg-6.0Gd-1.2Cu-1.2Zr (wt-%) alloy was designed and prepared by gravity casting, then the ingots were solution treated at different temperatures. The microstructures of the as-cast and solution-treated alloys were observed by optical microscopy (OM) and scanning electron microscopy (SEM). Corrosion behaviors were evaluated by immersion tests in simulated body fluid. It is indicated that the as-cast alloy is composed of α-Mg matrix, eutectic phase and lamellar long period stacking ordered (LPSO) structure. After solution treatment, the volume fraction of the LPSO structure increases first, then decreases and vanishes finally. The eutectic phase is distributed discontinuously in the alloys. The solution-treated alloys exhibit enhanced corrosion resistance compared with the as-cast alloy. In addition, the alloy after solution treatment at 360 °C shows the lowest corrosion rate. Quasi in situ corrosion tests demonstrate that the corrosion sequence is α-Mg, followed by the LPSO structure, and the eutectic phase in all alloys exhibits inappreciable variations during the corrosion test for 30 min.