Microstructure and Mechanical Properties of P-Modified Al–25Mg₂ Si–6Mg–11Cu–11Zn Alloy

We study the microstructure and precipitation behavior of P-modified Al–25Mg₂Si alloy with excess Mg, Cu, and Zn. The addition of P significantly refines the primary Mg₂Si phase (from 165 to 43 μm) due to enhanced heterogeneous nucleation at the Mg₃P₂ phase. This refinement leads to improvements in compressive strength (from 440 to 585 MPa) and fracture strain (from 3.0 to 3.6%). The solution-treated alloy containing partially spheroidized and smoothed secondary phases exhibits significant age hardening at both 25°C and 120°C. Transmission electron microscopy (TEM) and small-angle neutron scattering (SANS) analyses confirm the formation of Guinier-Preston (GP) zones, η', and η nanoprecipitates during aging at 120°C. Solution and subsequent peak-aging enhance the compressive strength (from 585 to 722 MPa) and fracture strain (from 3.6 to 4.0%) of the alloy.