Evolution of the Microstructure and Mechanical Properties of Mg-10Gd-2Y-0.5Zn-0.3Zr Alloy during Extrusion and Aging Processes

The evolution of the microstructure and mechanical properties of Mg-10Gd-2Y-0.5Zn-0.3Zr alloy during the extrusion process and aging process is analyzed in the present article. Compared with that of the forged alloy, the refinement of the microstructure and distribution of strengthening phases in the matrix are obvious, indicating that the extrusion process has a considerable effect on the microstructure and contributes to the excellent mechanical properties of the extruded alloy with a tensile yield strength, ultimate tensile strength and elongation of 306, 410 MPa and 16.3%, respectively. The microstructure and mechanical properties change considerably during the subsequent aging process compared with those of the extruded alloy. The strength of the peak-aged alloy has a great relationship with the strengthening precipitates in the matrix during the aging process. According to the qualitative analysis, the high strength of the peak-aged alloy at 200 °C for 120 h is mainly ascribed to the dispersed precipitates of the LPSO phase and β ′ phase during the aging process. With increasing temperature of the aging process, the dynamic softening of the alloy is mainly attributed to the following reasons: the phase transformation of the β ′ phase to the stable softening β phase, the coarsening of the LPSO phase and the decrease in the number of strengthening phases in the matrix. The tensile yield strength, ultimate tensile strength and elongation of the peak-aged alloy are 333 and 467 MPa and 7.6%, respectively.