Superior corrosion-resistant Mg-Gd-Zn-(Sn)-Zr Alloys: synergistic regulation mechanism of simple heat treatment and microalloying

• The addition of 0.2 wt% Sn promotes the very dense 14H-LPSO/SFs structure. • Dense LPSO/SFs structure reduces the corrosion rate by two orders of magnitude. • MgGdSn phase generated by excessive Sn seriously accelerates local corrosion. This study investigates the influence of Sn content on the microstructure and corrosion resistance of Mg-11Gd-1Zn-0.5Zr (GZ111) alloy. The results indicate a significant correlation between Sn content and the corrosion resistance in different alloy. Increasing Sn content continuously elevates the corrosion rate of as-cast alloys by disrupting the continuity of the (Mg, Zn) 3 Gd phase. In the as-homogenized GZ111-xSn (x = 0, 0.2, 1) alloy, the maximum potential differences between Zn 2 Zr 3 phase, 14H-LPSO/SFs structure, MgSnGd phase and α-Mg are 98, 31 and 68 mV, respectively. After Sn microalloying, a large number of weak anode SFs and low potential LPSO structures appeared in the as-homogenized GZ111-0.2Sn alloy, which formed a dense corrosion barrier and reduced the micro-galvanic corrosion, making the alloy show the lowest corrosion rate (0.077 mm·year −1 ).