Microstructure and mechanical properties of a heat-treatable Al-3.5Cu-1.5Mg-1Si alloy produced by selective laser melting

A heat-treatable Al-3.5Cu-1.5Mg-1Si alloy is successfully fabricated by selective laser melting and is investigated concerning microstructures and mechanical properties. The as-prepared samples show a fine-granular microstructure in the individual melt pool of the tracks and a coarse-granular microstructure in the areas between the tracks. After T6 heat treatment, the grain size of the specimens increases slightly and the Q phase formed in the as-prepared specimens transforms to Al₂Cu(Mg), Mg₂Si, and Al_xMn_y. All Al-Cu-Mg-Si specimens before and after heat treatment fracture around the defects that were generated during processing and show intergranular fracture along columnar grains upon tensile quasi-static loading. The as-fabricated samples exhibit a yield strength (YS) of 223 ± 4 MPa and an ultimate tensile strength (UTS) of 366 ± 7 MPa with an elongation of 5.3 ± 0.3%. After T6 heat treatment, the YS and UTS increase dramatically to 368 ± 6 MPa and 455 ± 10 MPa due to the formation of nano-sized Al₂Cu(Mg) precipitates, while the ductility remains fairly similar.