Influence of substructures on precipitation behavior and mechanical properties of cryogenic rolled Al–Mg–Si alloys during aging treatment

Cryogenic rolling is a promising method to improve the mechanical properties of Al–Mg–Si alloys. In this paper, the effect of artificial aging treatment on the mechanical properties and microstructures of cryogenic rolled Al–Mg–Si sheet is investigated. The hardness and yield strength of cryogenic rolled alloys decrease at the early aging stage, but the hardness and yield strength of room temperature rolled alloys increase at the early aging stage. Besides, substructures (such as dislocations) are observed in cryogenic rolled alloys but not in room temperature rolled alloys after solution treatment, the degree of recrystallization in the cryogenic rolled alloy is inferior to that in room temperature rolled alloy. The differences lead to the difference in strength between cryogenic rolled alloys and room temperature rolled alloys at the early aging stage. A precipitation mechanism is proposed to explain how these substructures promote precipitate nucleation and growth during artificial aging treatment. Based on the precipitation strengthening theory, a precipitation model is used to explain the strengthening contribution from precipitation during aging treatment, the capacity of precipitation strengthening in cryogenic rolled alloy is much higher than that in room temperature rolled alloy.