Microstructure and strengthening‑ductility synergy of Mg-Gd-Nd-Zn-Zr alloys in different states
摘要
This study investigated the microstructural evolution and mechanical properties of a novel Mg-4.0Gd-2.7Nd-0.6Zn-0.4Zr alloy during solution and aging treatments. A T6-treated alloy with an excellent strength-ductility balance was obtained. The as-cast alloy mainly consisted of α-Mg matrix, Mg12Nd and Mg3Gd phases distributed along the grain boundaries. After solution treatment at 515 ℃ for 12 h, the eutectic phases dissolved into the matrix, accompanied by the formation of a large number of Zn2Zr3 phases. The solution-treated alloy reached peak hardness after aging at 200 ℃ for 30 h and at 225 ℃ for 24 h. The alloy aged at 200 ℃ exhibited high strength, with a tensile yield strength (YS) of 223 ± 3 MPa and an ultimate tensile strength (UTS) of 323 ± 3 MPa, at the expense of ductility (5.3%). In contrast, aging at 225 ℃ resulted in a better strength-ductility balance, with YS and UTS slightly decreasing to 213 ± 5 and 304 ± 4 MPa, respectively, while elongation significantly increased to 14.3 ± 0.3%. The high strength but limited ductility at 200 ℃ was attributed to high anti-phase boundary energy arising from a small number of coherent β′′/β′ phases sheared by basal dislocations. In contrast, the semi-coherent β1 phases formed at 225 ℃ played a dual role by initially pinning dislocations to enhance strength and subsequently accommodating deformation via its own slip systems to improve ductility. These findings provided new insights into the design of high-performance Mg alloys with low rare earth content.