Tailoring microstructural evolution and surface durability of Al-6.8Si-4.2Cu-0.3Mg alloy via non-isothermal aging treatment

This study investigates the influence of non-isothermal aging on the microstructural evolution, mechanical properties, and tribological behaviour of a cast Al–6.8Si–4.2Cu–0.3Mg alloy. Following solution treatment at 520 °C for 12 h and water quenching, the alloy was subjected to continuous-heating aging at a rate of 60 °C h−¹ to peak temperatures of 120, 160, 200, and 240 °C. The results demonstrate that aging to 160 °C provides the optimum strengthening response through the formation of a fine, dense, and uniformly distributed population of coherent Al₂Cu precipitates while suppressing precipitate coarsening and delaying over-aging. In contrast, aging at temperatures below or above this optimum results in either insufficient precipitation or precipitate coarsening, thereby reducing strengthening efficiency. The optimised condition exhibits the highest hardness (142.3 ± 2.3 HV), ultimate tensile strength (335.7 ± 5.4 MPa), and tensile toughness (4.28 ± 0.21 MJ·m−³). In addition, it shows significantly improved tribological performance. This improvement is attributed to a transition from severe adhesive wear in the as-cast alloy to predominantly mild abrasive wear after optimised aging, reflecting enhanced surface stability and greater resistance to material removal.