Microstructural evolution and strengthening mechanism of Mg-Y-RE-Zr alloy fabricated by quasi-directed energy deposition

In this work, the highest yield strength and elongation in an Mg-Y-RE-Zr alloy produced by an additive manufacturing (AM) process is reported. A combination of a large-diameter welding wire and a pulsed current was used to inhibit the oxidation of WE43 alloy fabricated by quasi-directed energy deposition using electric arc (quasi-DED-Arc). The results show that the amount of Y2O3 in this work is only 2∼5% of that of the sample produced by powder bed fusion (PBF) reported previously. Moreover, the variable solidification conditions and in-situ heat treatments induced by the multiple thermal cycles (MTCs) were found to result in an inhomogeneous microstructure along the building direction, which are responsible for the variations in mechanical properties. The WE43 alloy exhibits excellent mechanical properties due to the intrinsic heat treatment that occurs during the build process. The 8th layer exhibits a maximum tensile strength of 347 MPa and a good elongation of 7.1%, which exceeds the strength-ductility combinations for cast WE43 alloy. The strengthening mechanisms in different layers have been discussed. A physical model depicting the microstructural transformation during quasi-DED-Arc has been proposed based on the measured thermal cycling data and microstructure observations.