Microstructure evolution and mechanical properties of a high-strength Mg-10Gd-3Y-1Zn-0.4Zr alloy fabricated by laser powder bed fusion

A high-strength Mg-10Gd-3Y-1Zn-0.4Zr (GWZ1031K, wt%) alloy was prepared by laser powder bed fusion (LPBF), and the microstructure and mechanical properties of the as built, LPBF-T5, LPBF-T4, and LPBF-T6 states were systematically studied. The as built alloy is composed of fine equiaxed alpha-Mg grains with an average grain size of 4.1 +/- 0.5 mu m, reticular beta-(Mg,Zn)(3) (Gd,Y) eutectic phase and flaky Y2O3 oxide phase, and exhibits yield strength (YS) of 310 +/- 8 MPa, ultimate tensile strength (UTS) of 347 +/- 6 MPa and elongation (EL) of 4.1 +/- 0.8%. A simple direct aging heat treatment at 175 degrees C for 64 h after LPBF leads to an ultra-high YS of 365 +/- 12 MPa but a low EL of 0.8 +/- 0.3% in the LPBF-T5 alloy. The solution heat treatment improves ductility by transforming the hard and brittle eutectic phase into the relatively soft and deformable lamellar long period stacking ordered (LPSO) structure inside grains and X phase at grain boundaries without obvious grain growth. Moreover, the LPBF-T4 alloy solution-treated at 450 degrees C for 12 h exhibits YS of 255 +/- 8 MPa, UTS of 328 +/- 9 MPa, and EL of 10.3 +/- 0.5%. Aging heat treatment after solution introduces numerous prismatic beta' and beta(1) precipitates, which help to increase tensile strength. The YS, UTS, and EL of the LPBF-T6 alloy are 316 +/- 5 MPa, 400 +/- 7 MPa, and 2.2 +/- 0.3%, respectively. It can be concluded that the LPBF process when combined with specially designed post-processing holds great promise for the manufacturing of high-performance components of the Mg-rare earth alloys with significantly higher YS for various applications.

Automated summary

A high-strength Mg alloy was prepared using laser powder bed fusion, and the microstructure and mechanical properties were studied in different states. The alloy exhibited improved strength and ductility after solution heat treatment and aging treatment.