Examining the impact of tool taper angle in Al-Si tube manufacturing by friction stir extrusion

Abstract

This study employed Friction Stir Extrusion (FSE) on the LM13 aluminum alloy to fabricate tubes using three distinct tool head designs: cylindrical, 30° taper, and 60° taper profiles. A comprehensive analysis of the microstructures and mechanical properties of the resulting samples was performed. A numerical study was conducted to model the process dynamics, focusing on temperature and strain distributions, material flow patterns, and the evolution of force, torque, strain, and strain rate. Findings indicated that the axial force with the cylindrical tool was 4–5 times greater than with tapered tools, while forces for the 30° and 60° taper tools were comparable. The 30° taper tool generated the highest strain value of 280 mm/mm, which significantly enhanced the mechanical strength of the pipe up to 139 MPa while it was 85 MPa in the base metal. However, the cylindrical tool had a much higher average strain rate of around 40 1/s, compared to below 10 1/s for the tapered tools, yet it was less effective at reducing porosity and breaking Si particles due to insufficient strain. Additionally, material flow patterns differed: with the cylindrical tool, flow moved from the periphery to the center, while tapered tools directed flow from the center toward the pipe wall.