Microstructure and mechanical properties of selective laser melting Al−Mg−Mn−Sc−Zr alloy annealed at different temperatures

Al−3.51Mg−0.42Mn−0.76Sc−0.40Zr (wt.%) alloy was prepared by selective laser melting (SLM) method. The mechanical properties and microstructure of the alloy after annealing at 300 °C or 325 °C for 6 h were studied. The tensile strength, yield strength and elongation of the SLM alloy were 339 MPa, 213 MPa and 24%, respectively. After annealing at 300 °C for 6 h, the tensile and yield strength of the alloy were increased to 518 MPa and 505 MPa, respectively, and the elongation decreased to 13%. After annealing at 325 °C for 6 h, the yield strength of the alloy was reduced to 483 MPa. The grain size of the alloy after annealing at 300 °C and 325 °C did not grow significantly, but the segregation of Mg element was significantly reduced. Nanoscale Al₃(Sc,Zr) phase was precipitated from the alloy matrix, and its average size increased with the increase of annealing temperature. Therefore, the strength improvement of the annealed SLM aluminum alloy was mainly attributed to the precipitation strengthening of Al₃(Sc,Zr), and the strengthening mechanism was mainly dislocation cutting mechanism. When the annealing temperature was too high, the coarsening of Al₃(Sc,Zr) particles caused the strength to decrease.