Microstructure evolution and strengthening mechanisms of high-strength Mg-5Al-1Mn-0.5Zn-0.5Ca by rotary forging

The high-strength Mg-5Al-1Mn-0.5Zn-0.5Ca alloy was fabricated via normal extruding and rotary forging (RF) in this study. The analysis focuses on the microstructure evolution and mechanical characteristics of the investigated alloy at different RF passes ( ε = 0.09, 0.16, 0.23). The optical microscopy and scanning electron microscopy experiments indicated that RF caused a remarkable decrease in grain size. As the RF strain increased, most of the Mg ₁₇Al ₁₂ and Al ₈Mn ₅ phases were crushed and dissolved back into the Mg matrix, eventually forming precipitations of nanoscale spherical Al-Mn and plate-shaped Al ₂ Ca particles. According to electron back-scatter diffraction, the fiber texture with the {0001} plane parallel to the feeding direction was formed after RF. Furthermore, tensile tests showed that RF significantly improved the mechanical properties of the investigated alloy bars. The forged samples at a strain of 0.16 exhibited lower cost and excellent strength characteristics, which were 417 ± 2 MPa of ultimate tensile strength, 370 ± 8 MPa of yield strength and a corresponding elongation of 8.6 ± 1.0%. The enhanced performance was attributed to the combined effects of dislocations, refined grains, second-phase particles and the suppression with basal slip. RF shows good potential for producing low-cost and superior-performance magnesium alloys, meeting the industrial requirement for strength as well as being suitable for massive production.