Friction stir processing: Impact on microstructure, mechanical behavior, and wear resistance of Al-9.2Si-4.9Cu-0.7 Mg alloy

This study investigates the influence of friction stir processing (FSP) parameters on the microstructure, mechanical properties, and wear behavior of an Al–9.2Si–4.9Cu–0.7 Mg alloy. Plates were processed at tool rotation speeds of 400–1000 rpm under a constant traverse speed of 40 mm/min. FSP effectively fragmented coarse eutectic networks and redistributed Si, Cu-, and Fe-rich intermetallics, while dynamic recrystallization refined grains to 5.2 ± 0.3 μm at 600 rpm and 7.1 ± 0.4 μm at 800 rpm. Peak stir-zone temperatures increased from 403 °C (600 rpm) to 457 °C (800 rpm), correlating with coarsening of θ-phase (Al 2 Cu) precipitates from 0.91 ± 0.03 μm to 1.21 ± 0.08 μm. Hardness improved markedly from the base alloy (≈108 HV) to 157.1 ± 1.2 HV at 600 rpm and 130.5 ± 2.7 HV at 800 rpm. Tensile strength rose from 273.5 ± 10.1 MPa in the as-cast state to 492.1 ± 10.2 MPa (P-600) and 371.8 ± 10.5 MPa (P-800), while elongation increased from 1.1 ± 0.4 % to 3.1 ± 0.9 % and 4.1 ± 0.8 %, respectively. Correspondingly, toughness improved more than fivefold, reaching 1436.2 ± 7.6 MJ m −3 at 600 rpm. Wear resistance was significantly enhanced, with wear rates reduced from 6.9 ± 0.2 μg/m in the base alloy to 4.1 ± 0.2 μg/m (600 rpm) and 4.8 ± 0.3 μg/m (800 rpm). The friction coefficient also dropped from 0.54 ± 0.03 to 0.37 ± 0.03 at 600 rpm.