Achieving strength-ductility synergy in Mg-Nd-Zn-Zr alloy fabricated by wire-arc directed energy deposition:La element addition via redox reaction of La_(2)O_(3) and MgOA

The application of the Mg-RE alloys in the aerospace field is often limited by their strength-ductility trade-off.In this study,the effect of La_(2)O_(3) with different mass percentages on the microstructure and mechanical properties of the wire arc directed energy deposition(WADED)manufactured Mg-Nd-Zn-Zr alloys was investigated.Among 4%,8%,and 12%La_(2)O_(3) specimens(the mass percentage of La_(2)O_(3) in the La_(2)O_(3)-alcohol solution),the 8%La_(2)O_(3) specimens produced a refined,equiaxed grain structure and the best strength-ductility synergy.At room temperature,the 8%La_(2)O_(3) specimens exhibited excellent strength-ductility synergy,and the UTS,YS,and EL of the as-deposited(AD)specimens were 243.38 MPa,141.81 MPa,and 22.15%,while the T6 heat-treated(T6)specimens achieved 334.71 MPa,222.08 MPa,and 19.36%,respectively.Compared to the room-temperature mechanical properties,the T6 heat-treated 8%La_(2)O_(3) samples at 250℃ maintain 66.21%in tensile strength,and the elongation increased by 4.81%.The enhanced strength-ductility synergy was achieved by incorporating the La elements during the WA-DED process,and the incorporation of La elements depended on a redox reaction:3Mg+La_(2)O_(3)→2La+3MgO.Notably,theβ1 phases(segregated Nd and La)were observed atγ1/Mg interfaces,underpinning a composite strengthening mechanism of the dislocation cutting mechanism and the dislocation bypass mechanism.These results provide a simple in-situ rare-earth reinforcement route to mitigate the strength-ductility trade-off in the Mg-RE alloys.