Strain path dependence of the precipitate size evolution of an Al–Mg–Li alloy under combined thermal and mechanical loading

The microstructural evolution during combined thermal and mechanical loading of an Al–Mg–Li alloy was studied. Hot tensile tests that followed or were preceded by annealing experiments without any applied stress, along with interrupted creep tests, were carried out. The δ′- and S1- precipitate structure was characterized by TEM. The results show that in the microstructural evolution, the path to reach a fixed strain plays an important role; for a high creep stress, the δ′-phase coarsens somewhat faster than under either combined thermal and mechanical loading or when isothermally aged without stress for the same time. The applied stress during creep affects the solute equilibrium concentration at the δ′/Al-matrix interface and modifies the local growth rate. The S1-phase is formed earlier in deformed microstructures due to heterogeneous nucleation at dislocations.