Effect of Heat Treatment on the Microstructure and Mechanical Properties of an Al-5mg2si-2mg Alloy Processed by Laser Powder Bed Fusion

The heat-treatment response of an Al-5Mg 2 Si-2Mg alloy fabricated by laser assisted powder bed fusion (L-PBF) was investigated for microstructural evolution and mechanical properties. The results showed that the solution at high temperature with subsequent ageing could not offer viable improvement in mechanical properties when applying 490 ºC/1 h for solution with different ageing processes. By contrast, significant improvement in strength was found in the L-PBFed Al-5Mg 2 Si-2Mg alloy after direct ageing at low temperatures, in which the yield strength increased from 295 MPa to 377 MPa and the elongation increased from 9.2% to 9.6% after ageing at the optimal condition of 180 ºC for 3.5 h. The improved mechanical properties are mainly attributed to the heritage of refined Al-Mg 2 Si eutectic network consisting of (a) Mg 2 Si eutectic phases between neighbouring fine Al sub-grains, and (b) in-situ Mg 2 Si nanoparticles formed during direct ageing for precipitation strengthening. However, the solution treatment breaks the Al-Mg 2 Si eutectic networks, and worsens the precipitation strengthening, resulting in the decrease in strength of this Al-5Mg 2 Si-2Mg alloy