Strengthening strategies for an Al alloy processed by in-situ alloying during laser powder bed fusion

In this work, a high strength Al alloy was successfully processed via in-situ alloying of AlSi10Mg and Cu elemental powders during Laser Powder Bed Fusion. To get superior strength, 4 wt% of Cu was added to AlSi10Mg composition to benefit from the additional solid solution and precipitation strengthening mechanisms induced by Cu atoms. Microstructure, chemical composition, hardness, and tensile properties of as-built samples were firstly determined. The microstructure showed a dual eutectic formed by Si precipitates intermixed with θ-Al2Cu phase. The average Cu concentration was 3.96 ± 0.26 wt% in line with the theoretical one. Hardness and yield strength of AlSi10Mg + 4Cu alloy showed an increase of respectively 8.8 % and 35.6 % compared to the as-built AlSi10Mg, owing to the highly super-saturated solid solution of Si and Cu atoms upon rapid solidification. After that, a direct aging heat-treatment strategy was pursued to fully exploit the potential alloy precipitation by heating as-built samples at temperatures between 160 and 190 °C. A maximum hardness response was achieved after 1 h at 175 °C. The high hardening was primarily attributed to a mix of θ''/θ'+θ-Al2Cu and Si phases coupled with a still high solid solution content. Nevertheless, direct aging slightly decreased the alloy ductility due to the prominent precipitation of brittle Si particles during aging and the presence of Cu inhomogeneities formed after in-situ alloying.