Remarkable strength-impact toughness conflict in high-strength Al-Mg-Sc-Zr alloy fabricated via laser powder bed fusion additive manufacturing

Laser powder bed fusion (LPBF) of AlMgScZr alloys have a combination of high strength and good ductility, which may apply to damage-tolerant structures. However, there have been only limited studies on the toughness performance of this promising alloy system. In the present work, the impact toughness of an LPBF-processed AlMgScZr alloy, which is critical for the application that involves high-strain-rate loading, was systematically investigated using instrumented Charpy impact testing. The results demonstrated that the AB(as-built)-LPBF-processed AlMgScZr alloy had a good combination of yield strength and impact toughness (338 ± 3 MPa, 27.47 ± 1.04 J), which were about 2 and 4 times those of the AC(as-cast)-processed AlMgScZr alloy (160 ± 1 MPa, 6.21 ± 0.66 J). However, post-aging treatment greatly deteriorated the impact toughness. On one hand, the strain-hardening capability of the LPBF-processed AlMgScZr alloy was reduced after post-aging; on the other hand, the coplanar slip associated with the L1₂ superlattice structure of the secondary Al₃(Sc,Zr) phase promoted the intergranular brittle fracture. This resulted in the remarkable strength-impact toughness conflict in the AA(as-aged)-LPBF-processed AlMgScZr alloy (512 ± 2 MPa, 4.27 ± 0.09 J). This study not only provides valuable insights into the dynamic fracture resistance of the LPBF-processed AlMgScZr alloys but also sheds light on the importance of choosing whether to post-age the LPBF-processed AlMgScZr alloy based on service loading conditions.