Laser Metal Fused Al Alloy Processed Using Different Heat Treatments

Abstract

Tensile and dilatometric specimens were obtained with longitudinal axis parallel to the building direction. A first set of samples has been directly aged in the as- built state (AB) while a second batch underwent solubilization annealing (SA) at 540°C for 60min just before artificial ageing (AA) at 160°C for 8h. Solubilization caused the precipitation of Si particles, suppressed by the rapid solidification during SLM. Moreover, it caused partial recrystallization leading to a coarser microstructure. The ageing response resulted very different in the two cases, involving a higher starting hardness for the as-built material, showing a markedly higher hardness during the whole process. In the as built (AB) material, isochronal ageing experiments carried out by differential scanning calorimetry showed the precipitation of Mg2Si particles beneath Si, while the same transformations were much less intense in the solubilized sample, due to the lower Si supersaturation. The ageing process raised the yield strength of about 20% compared to the AB material, slightly reducing the fracture elongation.