Microstructure and corrosion behavior of as-extruded Mg-6.5Li-xY-yZn alloys

The as-cast Mg-6.5Li-xY-yZn alloys (Mg-6.5Li-0.8Y, Mg-6.5Li-0.8Y-0.3Zn and Mg-6.5Li-1.0Y-1.0Zn) were extruded at 553 K with an extrusion ratio of 25:1 and a constant extrusion speed of 1.6 mm/s. The microstructure and corrosion behavior of as-extruded Mg-6.5Li-xY-yZn alloys were studied by microstructure observation, weight loss test, hydrogen evolution test and electrochemical test in present work. The microstructure shows that the Mg-6.5Li-0.8Y alloy contains α-Mg, β-Li and Mg2Y phase, the Mg-6.5Li-0.8Y-0.3Zn alloy is composed of α-Mg, β-Li and X phase (Mg12ZnY, LPSO phase) and the Mg-6.5Li-1.0Y-1.0Zn alloy consists of α-Mg, β-Li and W phase (Mg3Zn3Y2). The corrosion results indicate that the combining addition of Y and Zn can improve the corrosion resistance of Mg-6.5Li alloys and Mg-6.5Li-0.8Y-0.3Zn alloy with LPSO phase possesses the best corrosion resistance. The surface microstructure of test alloys after immersed in 3.5 wt% NaCl solution for 48 h, showing that the Mg-6.5Li-0.8Y alloy has the most corrosion pits while the Mg-6.5Li-0.8Y-0.3Zn alloy has the least corrosion pits due to the minimal micro-galvanic formed on its surface.