Revealing the corrosion mechanism of solid-state-recycled Mg-Gd-Y-Zn-Zr alloys through spark plasma sintering and hot extrusion

The study investigated the effects of hot extrusion and subsequent heat treatment on the microstructure and corrosion behavior of the solid-state-recycled Mg-Gd-Y-Zn-Zr alloy through spark plasma sintering. The results showed that the block LPSO phase in the AC-EX alloy exhibited lower potential than α-Mg matrix. Heat treatment promoted the precipitation of 14H-LPSO lamellae within the α-Mg matrix, significantly reducing the potential difference between block LPSO phase and α-Mg matrix. The hot extrusion can effectively eliminate the pores and improve the metallurgical bonding between chips of the solid-state-recycled alloys prepared through spark plasma sintering. The continuous RE oxides layers were broken into discontinuous particles, and some fine particles were dispersed into α-Mg matrix, which reduced connectivity of corrosion channels and suppressed corrosion propagation along the bonding interfaces, thereby improving corrosion resistance of the recycled alloy. The residual bonding interfaces in the SPS-EX sample obviously exhibited low-potential characteristics. The subsequent heat treatment caused the agglomeration of RE oxides, which result in the widening of bonding interface and affected zone. This increases the potential difference between bonding interface and α-Mg matrix, and aggravates localized corrosion of the adjacent matrix, resulting in the deterioration of corrosion resistance of SPS-EX-480°C/8 h alloy.