Recently, the team of Professor Qin Gaowu, School of Materials, Northeastern University, has made important progress in the research of low-cost magnesium alloy with high strength-ductility synergy. The "high strength and low-alloyed magnesium alloy" developed by the team has reached the highest strength in the world among the same kind of low-cost magnesium alloy, and successfully solved the bottleneck of mutual exclusion of strength and ductility of magnesium alloy, providing a new development path for the design of new high-performance deformed magnesium alloy materials. Relevant high-level research results have been published continuously in Acta Materialia, a top international journal of metal materials research, and have gained wide attention from researchers and industry both at home and abroad.
In recent years, based on phase equilibrium and thermodynamic calculation of magnesium alloy, the research team has discovered a new mechanism of grain refinement for the dynamic segregation of Ca solute induced by defects, and has successfully designed and prepared a series of Mg-Ca base alloys with excellent mechanical properties. In 2015, the tensile strength of Mg-Ca binary alloys can reach 330 MPa, which is ~ 100 MPa higher than that of Mg-Ca deformed alloys reported by Kim group of Korea, and the elongation can reach ~10% (J. Alloys Compd., 2015, 630:272-276). In 2017, Mg-Ca binary alloy was prepared based on traditional one-step extrusion. The grain size of the matrix can be further refined to ~0.7 μm, and the tensile strength at room temperature can reach ~400 MPa (Mater. Lett., 2019, 237:65-68). In 2018, the team found that adding a small amount of Ca to the conventional extruded Mg-2Ca-2Sn rare-earth-free alloy could induce the segregation of Ca at the grain boundary/subgrain boundary and the dynamic precipitation of nano-Mg2Ca. By giving full play to the alloying elements and the fine crystallization of the extrusion process, the α-Mg matrix was refined to a submicron size (~0.32μm) which is difficult to achieve by conventional extrusion. Thus, excellent mechanical properties (yield strength ~443 MPa) were demonstrated (Fig. 1). The alloy can obtain ultra-high strength at a solute content of~4wt.%, that is to say, "high-strength and low-alloyed magnesium alloy" was achieved (Acta Materialia, 2018, 149:350-363).
Figure 1. Microstructure Characteristics of Ultra-high strength Ca-containing Deformed Magnesium Alloy
In order to overcome the problem of mutual exclusion between strength and ductility of magnesium alloys, the research team recently put forward a new design idea of magnesium alloys with high density and low energy interface based on dynamic segregation of multi-component solute elements. Mg-Ca-Al-Mn-Zn extruded alloy (total solute content ~2.4 wt.%) has achieved yield strength of ~425 MPa, tensile strength of ~442 MPa, elongation of ~11% (Acta Materialia, 2020, 186:278-290).
Figure 2. Microstructure and Performance Characteristics of a New Low-Cost Mg-Ca-Al-Zn-Mn Alloy with High Strength-Ductility
Based on the idea of dynamic segregation of solute atoms in crystal defects mentioned above, the research team will further combine the first principle, molecular dynamics and phase diagram calculation to design and prepare a low-cost deformed magnesium alloy material with high strength-ductility synergy and better comprehensive performances to meet the practical needs of engineering in different fields.