The Influence of Velocity and Pressure on Residual Stresses During The Backward and Forward Extrusion of AA6061 T6 Aluminium Alloy

The extrusion process is considered a cost-effective manufacturing method compared to alternative production techniques, offering excellent mechanical properties and high product quality. Combined extrusion further enhances efficiency by minimizing the need for additional processing steps, thereby saving time and reducing production costs. The die geometry and friction factors play a critical role in determining the success and quality of this process. In this study, AA 6061 T6 aluminium alloy was selected as the billet material to investigate a combined backward–forward extrusion process and to examine the influence of process parameters, such as velocity and pressure, on the residual stresses formed in the extruded products. Two punch types were utilized: a hexagonal punch for the backward extrusion direction and a square punch for the forward extrusion direction. For each punch type, three different cross-sectional areas (140, 130, 115 mm2) and three different forming velocities (0.25, 0.5, 1 mm/s) were tested to assess the effect of forming pressure on residual stresses. The experiments were conducted using a heat-treated H13 steel die with a hydraulic press under lubricated conditions. The findings indicate that increasing the cross-sectional area of the punch, which corresponds to a reduction in pressing pressure, results in higher residual stresses at a constant velocity. The highest residual stresses were observed in the hexagonal region (1315 MPa), corresponding to the backward extrusion process. Intermediate stress levels (