Toughening the additively manufactured Al alloys via manipulating microstructural heterogeneity

Achieving high strength and simultaneously high toughness of Al alloys remains challenging. Recent studies show that structural heterogeneity derived from additive manufacturing process is effective to improve mechanical properties of Al alloys. In this paper, the elaborately designed Al alloys with compositions of Al-Fe-Cu-xZr (x = 0.6, 0.8 and 1.3 at %) are subjected to laser powder bed fusion (LPBF). It is found that all three alloys show obvious heterogeneous structures with two distinct zones, i.e., coarse grain zones (CGZs) and fine grain zones (FGZs), where the FGZs have significantly higher hardness than the CGZs do. The grain size in both CGZs and FGZs decreases with increasing Zr content, and causes significant variation of mechanical properties. The Al-Fe-Cu-0.8Zr alloy exhibits the best combination of high yield strength and plasticity as well as the high resistance to crack propagation (corresponding to high fracture toughness). The enhancement of fracture toughness is mainly attributed to a sharp difference in local hardness at the interfaces between FGZs and CGZs. This work provides a promising strategy for toughening the additively manufactured Al alloys.