Effect of non-isothermal ageing on microstructure and mechanical properties of an Al–Cu–Mg–Ag alloy

The effect of non-isothermal ageing (NIA), combined with two conventional T6 treatments on the microstructure and mechanical properties of an Al–Cu–Mg–Ag alloy was investigated. Tensile results indicate that both NIA treatments can modify the strength properties (∼8 and ∼20 MPa for yield strength, respectively) despite the slight decrease in elongation (∼2 and ∼1%, respectively) compared with the optimal T6 treatment (165T6). The decreasing elongation to failure was attributed to the variation in the width of PFZs. Quantitative measurements showed that the microstructural parameters of Ω phases (diameter, number density and volume fraction) varied under different ageing treatments, and the corresponding contribution to yield strength was estimated by a precipitate strengthening model proposed by Nie and Muddle. Interestingly, heterogeneity in the size distribution in the NIA and 200T6 alloys was found to be manifest compared with that in the 165T6 alloy. The origin of the microstructural features was discussed in detail.