Microstructural evolution, mechanical behaviour and strengthening mechanisms of additively manufactured AlSi9Cu3 alloy

Additive manufacturing (AM) offers a significant advantage over traditional methods by enabling the fabrication of complex geometries and lightweight components. This weight reduction capability, coupled with the high strength-to-weight ratio of aluminium alloys, makes the additive manufacturing of aluminium alloys very attractive. However, the material selection for additive is very limited; hence, this study investigates the mechanical properties, precipitate evolution, and microstructure-property correlation of the AlSi9Cu3 alloy. Despite having significant applications and good printability in additive manufacturing, the mechanical properties and microstructural features of AlSi9Cu3 fabricated using Laser Powder Bed Fusion (LPBF) have not been well explored. The main aim of this paper is to investigate the static properties, such as tensile, hardness and fracture toughness and correlate them with different microstructural features and strengthening mechanisms. The printed specimen showed superior mechanical performance with a yield strength of 235 ± 9.5 MPa, an ultimate tensile strength of 410 ± 5.2 MPa, and ductility of 6.1 ± 1.4 %, which is much higher than that of the as-cast AlSi9Cu3 alloy. These superior properties were attributed to the refined microstructure formed during additive manufacturing, an eutectic Si network formed due to cyclic thermal exposure, and θ (Al 2 Cu) strengthening precipitate in the additively manufactured alloy. These findings highlight the potential of AM to enhance the performance of AlSi9Cu3 alloys for advanced structural applications across industries.