Microstructural Evolution and Mechanical Properties of AE45-Gd Magnesium Alloy Under Different Aging Processes

To investigate the microstructural evolution and mechanical property changes in an as-extruded AE45-Gd magnesium alloy subjected to different aging treatments, an alloy containing multi-scale second phases was prepared by extrusion and subsequently subjected to artificial aging and aging under pressure. The microstructural evolution, age-hardening behavior, and mechanical properties of the alloy under different aging treatments were investigated. It was found that conventional isothermal aging can improve the mechanical properties to a certain extent. As the aging temperature increases, the peak-aged hardness decreases slightly, while the time to reach peak aging is progressively shortened. Aging under pressure also significantly shortens the time to peak aging, though the peak-aged hardness changes little. The multi-scale second phases in the alloy, consisting of coarse blocky Al₂RE (La, Ce, Gd) and fine granular Al₁₁RE₃ (La, Ce, Gd), exhibit typical Ostwald ripening during aging, and aging under pressure accelerates this process. The optimum aging parameters are determined to be 200 °C for 16 h. After this treatment, the alloy achieves a yield strength of 183.95 MPa, a tensile strength of 322.50MPa, and an elongation of 4.32%. Microcracks predominantly initiate at the large Al₂RE (La, Ce, Gd) compounds. The small granular Al₁₁RE₃ (La, Ce, Gd) particles show little evidence of self-cracking, and cracking mainly occurs at the phase boundaries between these particles and the magnesium matrix.