Effect of solid solution plus double aging on microstructural characterization of 7075 Al alloys fabricated by selective laser melting (SLM)

The microstructure, hardness and phase transformation of 7075 aluminum alloy fabricated by selective laser melting (SLM) under solid solution plus double aging were studied by using optical microscope (OM), micro-hardness tester, scanning electron microscope (SEM) and transmission electron microscope (TEM). The test results show that microstructures of as-received alloy present the obvious uneven inter-channel structure. When the solid solution plus double aging were used, the alloy shows the homogeneous refinement structure. The inter-channel structure of the alloy completely disappeared. The hardness under the solid solution plus double aging also increased compared with the as-received alloy (HV80), and the average hardness is about HV158. Some typical S phase (Al2CuMg) and theta phase (Al2Cu) precipitated at the grain boundary, which has a significant effect to improve the hardness of alloys via the dispersion strengthening and precipitation strengthening.