Microstructure and mechanical properties of Zr-modified aluminum alloy 5083 manufactured by laser powder bed fusion

Aluminum alloy (AA), AA5083 and AA5083 alloyed with 0.7 wt.% Zr (hereafter denoted as AA5083+Zr) were manufactured by laser powder bed fusion (LPBF) using gas atomized powders. Parametric investigation was performed by using laser powers of 200 W and 350 W with various scan speeds. AA5083 alloy was difficult to manufacture by LPBF due to formation of excessive pores or solidification cracking or compositional deviation due to evaporation at all processing parameters examined, i.e., poor buildability/printability. However, with the addition of 0.7 wt.% Zr, the AA5083+Zr alloy was manufactured with near-full density, without solidification cracks and with proper composition. The as-built AA5083+Zr alloy exhibited outstanding tensile properties with yield strength of 212 MPa, tensile strength of 317 MPa and elongation of 22.3%. After heat treatment at 400 °C for 2 h, the yield and tensile strength of LPBF AA5083+Zr alloy increased to 319 MPa and 392 MPa, respectively, although the elongation reduced to 14.1%. Microstructural analyses revealed a dramatic difference in grain size and distribution between the as-built AA5083 and AA5083+Zr alloys. The primary, pro-peritectic Al₃Zr particles were observed at the melt pool boundaries, which would refine the grains in the as-built AA5083+Zr alloy, and help eliminate the solidification cracking. Furthermore, a significant amount of nano-scale (˜3 nm) Al₃Zr precipitates were observed within the grains after the heat treatment of AA5083+Zr alloy, which would contribute to the increase in strength observed. A qualitative processing map correlating the porosity/cracks and laser power/scan speed is proposed and discussed with respect to the effect of Zr on the refinement of microstructure and improvement of buildability/printability.