Near peak-aged strengthening of Al-Mg-Si-Cu alloys by extrusion-induced in-situ precipitation via short-process powder metallurgy

Conventional powder metallurgy (PM) processing of Al-Mg-Si-Cu alloys generally relies on solution-aging (T6) treatment to activate precipitation strengthening, resulting in long processing cycles and high cost. Here, a short-process PM strategy is developed by coupling rapid solidification with extrusion-induced in-situ precipitation to directly generate a near peak-aged microstructure. Gas-atomized Al-5.0 Mg-0.5Si-(0.5/1.0)Cu powders exhibit fine cellular structures and high solute supersaturation. Hot extrusion at 300 °C simultaneously consolidates the powders, induces dynamic recrystallization, and activates in-situ precipitation, producing refined equiaxed grains and a high density of strengthening precipitates. The Al-5.0 Mg-0.5Si-0.5Cu alloy achieves an ultimate tensile strength of 396.8 ± 1.7 MPa, a yield strength of 250.6 ± 1.7 MPa, and an elongation of 11.9 ± 1.1% directly in the as-extruded state, with only marginal softening after subsequent aging. TEM reveals that strengthening is dominated by coherent nanoscale β″/β′ precipitates, supplemented by coarser β (Mg 2 Si) and Al 2 CuMg phases. In contrast, solution treatment causes precipitate coarsening, density loss, and oxygen uptake, resulting in inferior properties. This work demonstrates a simplified and scalable route for producing high-strength, ductile Al-Mg-Si-Cu alloys without conventional T6 treatment.