Processability improvement and strength enhancement in laser powder bed fusion of AlMgZr and AlMgZr-Ti alloys

Abstract

The Al3(Ti, Zr) phase, which exhibits a lower formation enthalpy, was incorporated to improve the processability and strength of AlMgZr alloys fabricated by laser powder bed fusion (PBF-LB). The results confirmed that the crack-free AlMgZr-Ti alloy exhibited a relative density of 99.7% and a fine grain size of ∼ 2.5 μm. The improved processability can be attributed to grain refinement and the columnar-to-equiaxed transition (CET), which is induced from promoted heterogeneous nucleation by in-situ Al3(Ti, Zr) phase and high grain growth restriction factor by segregation of Ti at the interface. During solidification, Al3Ti phase was precipitated initially and Zr was incorporated into the Al3Ti lattice in the subsequent precipitation, accelerating Zr precipitation from α-Al matrix. Through experimental results and calculations of formation enthalpy in combination, the Al3(Ti, Zr) phase was most likely to be Al3(Ti5/6, Zr1/6). Meanwhile, the AlMgZr-Ti alloy exhibited superior strength in comparison with the counterpart of AlMgZr alloy, where the enhancement of YS (408 MPa) and UTS (432 MPa) is 119% and 42.6%, respectively, with the UTS of the AlMgZr-Ti alloy maintaining 182 MPa at 300 °C.