Creep response of strip-cast Al-1wt.% Mn-1wt.% Mg alloy to thermomechanical treatment

Abstract

Strip-cast Al-1wt.%Mn-1wt.%Mg was subjected to thermomechanical treatment (TMT) in order to combine a dislocation substructure of submicron initial subgrain size L₀ with phase structures hardening, manganese either being participated or not. The influence of TMT on the mechanical properties was investigated between room temperature and 573 K by means of tests at a constant elongation rate and creep tests. The microstructure was investigated using transmission electron microscopy. TMT enhances the room temperature yield strength σ_y according to σ_y = σ⁰ + kL₀⁻¹ where σ⁰ and k are constants. At elevated temperatures the maximum strength is reached under most conditions after a small amount of strain (a few per cent). This is due to the microstructural changes that accompany deformation. The subgrain size changes during deformation from L₀ towards a steady state value L_s, which in material which has no precipitated manganese is inversely proportional to stress. Under conditions where L_s ~ L₀, substructural hardening is prominent. However, for L_s ≫ L₀, there is virtually no hardening effect. Under intermediate conditions there is an initial strain range in which the specimen work hardens while the substructure coarsens. This is interpreted in terms of glide associated with recovery of the dislocation structure.