Effects of different combinations of artificial ageing and warm forming on Ω phase and S phase evolutions in an Al-5.1Cu-1.0Mg-0.4Ag high strength aluminum alloy

Unlike common age-hardening materials, deformation prior to artificial ageing has been found to adversely affect the hardness of AA2040 aluminum alloy. To prevent this disadvantage, the effects of four different combinations of warm forming and artificial ageing at 200 °C on the microstructures and Vickers hardness of Al-5.1Cu-1.0Mg-0.4Ag aluminum alloy have been investigated. Among the four different combinations, the combination of 5% warm forming +1 h ageing yielded the lowest hardness value (154 HV), while that of 40 min ageing + 5% warm forming + 20 min ageing yielded the highest (169 HV). It is presumed that the proper timing of inducing dislocations by warm forming is decisive. The appropriate combination of warm forming and artificial ageing, i.e., 40 min + 5%+20 min treatment, produces a suitable amount of Ω phase during the first-stage ageing (40 min ageing), induces dislocations in the subsequent warm forming (5% deformation), and causes the significant amount of lath-like S phase to form on dislocations during the final-stage ageing (20 min ageing), thus enhancing the overall mechanical strength.