THE EFFECT OF POST PROCESSING ON THE MECHANICAL PROPERTIES AND FRACTURE MECHANISMS OF ALSI10MG PRODUCED THROUGH SELECTIVE LASER MELTING

Abstract

The use of selective laser melting for AlSi10Mg has been gaining a lot of popularity, but unfortunately, there are a great deal of issues surrounding internal porosity. Hot isostatic pressing (HIP) has been used in many instances alongside a standard T6 treatment to reduce porosity, but that typically involves water quenching. The application for this project is meant for the satellite industry, which has tight dimensional tolerances and as such, water quenching is not adequate. Currently, annealing for a stress relief treatment is the only post- processing measure that does not involve water quenching. This project studied a novel direct HIP approach, whereby an argon quench is used after solution annealing. Three different cooling rates were studied within the DHIP process (DHIP-L=50°C/min, DHIP- M=200°C/min, and DHIP-H=400°C/min) and compared to specimens that were stress relieved (SR). Uniaxial tensile testing revealed that the strength and ductility of DHIP-H outperformed the SR condition. The true stress/strain results showed that all DHIP conditions had a superior true strain and true stress at fracture. All DHIP conditions and SR showed evidence of void growth and coalescence. SR fracture is driven through crack initiation, while the DHIP conditions fracture is driven through localized necking. In-situ tensile tests via scanning electron microscopy coupled with μ-DIC revealed that the DHIP conditions feature damage due to particle fracture, while the SR condition experiences strain localization along the interface of Si particles and the α-Al phase. In-situ tensile testing via XCT studied a comparative analysis between DHIP-M and SR and revealed that DHIP-M experiences more void growth and nucleation than the SR condition.