Exploration of a new manufacturing process for improving mechanical properties in a hot extruded Al-Mg-Si alloy

Abstract

Al-Mg-Si alloys are age-hardenable and exhibit a good strength-to-weight ratio, formability, corrosion resistance, making them widely used in commercial applications. In particular, Al-Mg-Si alloys with high strength and elongation are preferred in the automotive industry. Components such as body sheets and bumper beams are typically manufactured by rolling or extrusion of billets, followed by artificial aging for strengthening. In conventional processing routes, billets are produced by casting prior to subsequent deformation. However, the cooling rates during casting and homogenization treatment processes are relatively slow. Such slow solidification conditions often promote the formation of coarse (microscale) secondary phases, such as intermetallic compounds and precipitates, which negatively affect the mechanical properties, particularly strength and ductility. To address this, the present study explores the use of laser powder bed fusion (LPBF), an additive manufacturing method, to fabricate billets for subsequent hot-extrusion. LPBF enables rapid heating and cooling of a material over a very short period. This rapid solidification can effectively suppress the formation of coarse secondary phases, thereby improving age-hardenability and enhancing both strength and ductility. This research work discusses insights into the mechanical property as well as the macro- and microstructural characteristics of a hot-extruded Al-Mg-Si alloy using an LPBF-fabricated billet. Compared with conventionally extruded aluminum, the material produced via the proposed LPBF-based route exhibited higher tensile strength and yield strength in the longitudinal direction while maintaining comparable ductility. Furthermore, the extruded alloy processed from the LPBF billet showed a finer grain size, which contributed to its enhanced strength relative to the conventionally extruded counterpart.