Microstructural evolution during the heat treatment of Laser Beam Melted AlSi10Mg

Al alloy AlSi10Mg processed by Laser Beam Melting (LBM) exhibits a much finer microstructure than its cast counterpart due to the ultra-fast cooling rates imposed in the LBM process. One important consequence of this microstructural refinement is that a classical T6 age hardening heat treatment will not have the same effect on LBM AlSi10Mg when compared with cast AlSi10Mg. Indeed, a previous study by the present authors has shown that heat treating LBM AlSi10Mg at 510°C for 6 hours followed by a second isothermal hold at 170°C for 6 hours brought a marked improvement of the yield stress by 30% and of the elongation at break by 220%. However, this was achieved at the expense of a decrease in both hardness and ultimate tensile strength. A better understanding of the underlying phenomena is needed in order to optimize the heat treatment of LBM AlSi10Mg. The present work hence aims at investigating in more depth the microstructural evolution induced upon heat treating LBM AlSi10Mg. Changes in texture as well as in the distribution of Si-rich precipitates (size, morphology...) have been studied, with a particular attention to those changes taking place during the first step of the heat treatment at the higher temperature of 510°C.