Improvement of strength and fracture toughness of a spray-deposited AlCuMgAgMnTiZr alloy by optimized heat treatments and thermomechanical treatments

Optimized heat treatments and thermomechanical treatments have been developed in order to improve the strength and toughness of a spray-deposited alloy Al-5wt.%Cu-0.4wt.%Mg-0.4wt.%Mg-0.4wt.%Ag-0.4wt.%Ti-0.15wt.%Zr-0.2wt.%Mn: (i) a two-step aging heat treatment consisting of artificial underaging at an intermediate temperature (160 °C) followed by peak aging at 210 °C; (ii) thermomechanical treatments implying cold rolling (8%) before artificial aging to peak hardness at 160 °C. ed with the conventionally peak-aged T6 temper, fracture toughness can be considerably increased by the two-step aging treatment, whereas the strength is slightly lowered. However, simultaneous improvement in both fracture toughness and yield strength results from the thermomechanical treatments; thus excellent combinations of fracture toughness and yield strength are achieved (Rp0.2 = 532 MPa and KIC = 47 MPa m12). tructure investigation by transmission electron microscopy reveals that the Al-Cu-Mg-Ag-based alloy is strengthened by comparable amounts of precipitates of type Ω and θ′. However, in accordance with the different mechanical properties of the various tempers, evident quantitative and qualitative differences in the precipitation state are observed: compared with the original T6 temper, the total amount of Ω and θ′ is decreased in the two-step-aged material, but both precipitates are much finer; the thermomechanically treated material shows the finest precipitate sizes altogether with the highest precipitate densities.