The effect of the extrusion process on the microstructure, corrosion, and mechanical properties of Mg–Zn–Ca–Zr alloy has been investigated. Zn and Ca were both in a solid solution and only the Zr-rich phase was observed in the homogenized and extruded alloys. The Zr-rich phase was obviously refined after extrusion. The corrosion rate of the homogenized alloy decreased by about 25% after extrusion. This is because the refined Zr-rich phase was easier to cover with the deposited corrosion products, which reduced the cathodic reaction activity of the Zr-rich phase. The corrosion rate is similar for the alloys extruded at 320 °C and 350 °C since the size and distribution of the Zr-rich phase were not different in the two conditions. The alloy extruded at 320 °C has a smaller grain size and better comprehensive mechanical properties.

The cathodic hydrogen evolution ability of different pure metals and their long term galvanic corrosion behavior with pure Mg were investigated. The hydrogen evolution ability of pure Ti, Al, Sn and Zr is weak, while that of Fe, W, Cr, and Co is very strong. Initial polarization test could not completely reveal the cathodic behavior of the tested metals during long term corrosion. The cathodic hydrogen evolution ability may vary significantly in the long term galvanic tests for different metals, especially for Al whose cathodic current density reduced to 1/50 of the initial value. The anodic polarization shows that Al and Sn as alloying elements are supposed to provide relatively good passive effect for Mg alloy, while Ag can provide a slight passive effect and Zn has little passive effect.