Temperature-dependent strain hardening, precipitation and deformation-induced microstructure evolution in AA 6061

The effect of β′′ precipitation on strain hardening and yield stress evolution in an A6061 aluminium alloy is studied experimentally and through thermokinetic computer simulation. Samples were deformed by compression at temperatures from 25 to 500 °C to strains of about 0.4 and three different precipitation states. Simulations on the thermal stability of β′′ are conducted on an equivalent model Al-Mg-Si alloy resulting in an explanation for the experimentally observed softening at intermediate temperatures. EBSD micrographs confirm that different dislocation storage and annihilation mechanisms are operative at low and high temperatures. The low temperature microstructure correlates very well with the subgrain structures typically observed during stage IV strain hardening.