Effects of Extrusion Treatment and Calcium Addition on the Microstructure and Corrosion Resistance of Mg-7Sn Alloy

The effects of extrusion treatment and addition of alloying element Ca on the microstructure, corrosion resistance and mechanical properties of Mg-7Sn alloy were studied by optical microscopy (OM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemical test and immersion test.The results showed that the addition of Ca element could significantly refine the grains of the cast Mg-7Sn alloy, and form rod-shaped CaMgSn with grain boundaries within the grains. At the same time, during the corrosion process, the addition of Ca could form compounds containing Ca on the alloy surface, prevent or delay corrosion, and improve the corrosion resistance of the alloy. The extrusion treatment reduced the average grain size of the alloy from 55.2 μm to 3.3 μm, and the coarse rod-shaped CaMgSn phase was broken into small blocks. After extrusion treatment, the corrosion resistance of Mg-7Sn-1Ca alloy slightly decreased, but high microhardness was ensured. The extruded Mg-7Sn-1Ca alloy exhibited both good mechanical properties and corrosion resistance.