Effect of Er Addition and Heat Treatment on Microstructure, Mechanical Properties and Corrosion Behaviors of As-Cast Mg-5Sm-0.2Ni Alloy

In this study, the synergistic influence of Er alloying and heat treatment on the as-cast Mg-5Sm-0.2Ni alloy were comprehensively investigated. The results show that Er addition promotes the formation of a Mg(Er,Sm)3 phase during the solidification process, and subsequent heat treatment alters the morphology, distribution and volume fraction of the Ni-containing LPSO phases, meanwhile promoting the precipitation of noodle-like Mg3Sm phases from an α-Mg matrix. Compared to the as-cast Mg-5Sm-0.2Ni alloy, the yield strength of the Mg-5Sm-1Er-0.2Ni alloy subjected to heat treatment increased from 88 ± 4 MPa to 144 ± 5 MPa, and the corrosion rate decreased from 492.6 ± 14.2 mm/year to 166.2 ± 12.4 mm/year. The enhanced yield strength of the heat-treated Mg-5Sm-1Er-0.2Ni alloy mainly originates from the finely dispersed Mg(Er,Sm)3 phases and the noodle-like Mg3Sm precipitates, while the reduced corrosion rate is due to the decreased volume fraction and coarsened size of the LPSO phases, which weaken the galvanic corrosion effect. This study provides a new approach for the preparation of Mg-Sm-Er-Ni alloys with high yield strengths and controlled corrosion rates.