Effects of different hot extrusion processes on corrosion behavior of Mg-6Gd-1Zn-0.5Zr alloy in 3.5 wt% sodium chloride solution

Poor corrosion resistance of magnesium alloy has become the main reason for limiting its application in the field of marine engineering. The aim of this study was to investigate the effects and causes of four different hot extrusion approaches on the corrosion properties of Mg-6Gd-1Zn-0.5Zr alloys in 3.5 wt% sodium chloride solution. The corrosion mechanisms were investigated through immersion experiments, electrochemical property assessments, and material characterization techniques such as OM, SEM, XRD, EBSD, CLSM, and XPS. Controls for comparison were provided by using as-cast and homogenous alloys. The findings suggest that the GZ61K alloy exhibits improved resistance to corrosion when extruded at angles of 120 degrees and 105 degrees but experiences a drop in corrosion resistance when forward extruded or extruded at an angle of 90 degrees. The primary cause of this phenomenon is the existence of stratified 14H-LPSO structures within the extruded alloy. The influence of the 14HLPSO structure on alloy galvanic corrosion is more pronounced than its impact on inhibiting corrosion propagation. As the concentration of the 14H-LPSO structure increases, the resistance to corrosion diminishes. Moreover, the existence of the twinned structure in the extruded alloy dramatically reduces its ability to resist corrosion.