Investigation of microstructure and mechanical properties of welds in wide stiffened panels from an innovative multi-container extrusion technology

Abstract

The emerging multi-container extrusion, known for its notable advantage of low extrusion force requirements, offers an opportunity to produce profiles with wider cross-sections. However, the presence of intrinsic welding defects and their impact on the profile quality have not been properly studied, which limits its wider industrial application. This study aims to characterise the weld microstructures and mechanical properties of profiles produced through multi-container extrusion by conducting a series of consecutive extrusion tests under varying temperatures and speeds, followed by post-extrusion microstructural analysis and tensile tests. The findings reveal that longitudinal weld (L-weld), formed by bonding adjacent billets, becomes indistinguishable and exhibits a uniform microstructure similar to the matrix material. In addition, a pair of transverse welds (T-welds) are formed by bonding the current billet to the previous one during the consecutive extrusion process, with their gap narrowing along the extrusion direction. Microscopically, T-welds are distinct, with their width increasing with the number of consecutive extrusions, due to their differing microstructure compared to the matrix material. Macroscopically, T-welds demonstrate much lower welding quality compared with L-weld, as evidenced by all tensile specimens with welds fracturing at the T-weld without displaying the necking seen in specimens without welds. Furthermore, in specimens without welds, representing the matrix material area of the extruded profile, yield strength (YS) and ultimate tensile strength (UTS) are more sensitive to extrusion speed, while elongation is more affected by extrusion temperature.