Precipitation behavior and mechanical properties of a Mg-Zn-Y-Zr alloy processed by thermo-mechanical treatment

Mg92Zn6Y1.5Zr0.5 alloy was extruded at 300, 350, 400 °C and then aged at 180 °C. In the extruded alloy, polygon- and bar-shaped precipitates were observed. The precipitates were identified as I-phase (Mg3Zn6Y) and W-phase (Mg3Zn3Y2) respectively by selected area diffraction (SAD) pattern. These precipitates played a role of strengthening the extruded alloy. After aging treatment for 24 h (peak-aged), intermetallic compounds identified as Mg2Zn11 and MgZn2 precipitate dispersively in the extruded alloys. The increase of yield strength at room temperature and ultimate strength at elevated temperatures after the aging process has been ascribed to the strengthening effect of these precipitates. After aging treatment for 48 h (over-aged), metastable phase Mg2Zn11 and MgZn2 transformed to stable phase MgZn phase, losing the coherence with the matrix.