Microstructural evolution and strength enhancement in laser powder bed fusion Al-Mg-Yb-Zr alloys

Abstract

Al-Mg alloys fabricated by laser powder bed fusion (L-PBF) usually suffer from poor processability and strength response. In this work, the effect of Yb and Zr in Al-Mg alloys was studied using Al-3Mg-0.7Zr and Al-3Mg-0.5Yb-0.7Zr alloys fabricated by L-PBF. The size of average grain along the building direction was measured to be 3.6 μm, of which 94.2 % consisted of equiaxed grains. The formation of Al3(Yb,Zr) phase in the L-PBF was revealed through single-track and multi-track melt pools and the formation of Al3Zr, Al/Al3Yb eutectics, in couple with the L12-Al3(Yb,Zr) phase were found to be responsible for the high-volume fraction of refined equiaxed grains. After aging at 375 ℃ for 14 h, a high-volume fraction L12-Al3(Yb,Zr) (4.5 nm) was formed within the relatively coarse grains (5.8 μm), which showed strong thermal stability and precipitation strengthening. As such, the as-aged Al-3Mg-0.5Yb-0.7Zr alloy can deliver a good combination of strength-ductility, in which ultimate tensile strength (UTS) and elongation (El) are 401 MPa and 15.1 %, respectively.