Effects of re-ageing treatment on microstructure and tensile properties of solution treated and cold-rolled Al-Cu-Mg alloys

The effects of re-ageing (RA) at different temperatures on the tensile properties and microstructures of the Al 2024 alloy (Al-Cu-Mg series alloy) were investigated, which had been solution treated (ST) at 495 °C for 1 h and conventionally cold-rolled (CR) with 83% thickness reduction. The strength of the alloy could be increased markedly by the thermo-mechanical treatment while maintaining acceptable ductility. The ultimate tensile strength (UTS), yield strength (YS) and elongation to failure (Ef) of the RA sample at 100 °C for 72 h were 755 MPa, 711 MPa and 7.3%. As comparison, the UTS and YS values of the conventional peak-aged (PA) sample at 190 °C for 8 h were 528 MPa and 426 MPa, respectively, with the Ef value of 13%. The quantitative estimation indicated that the high strength of the RA samples was attributed to the combined effects of dislocation, precipitation, grain size and texture strengthening mechanisms. Microstructure observations revealed that the ductility of the RA samples could be improved by the GBP zones rather than S′ phase. Fractography observations displayed that the precipitation of S′ phase accelerated the tensile failure of the RA samples by microvoid coalescence, whereas the precipitation of GPB zones would not.