Effect of deformation on precipitation in Al–Mg2Si alloys containing silicon in excess

The aging behavior of 17 kinds of Al–Mg2Si alloys containing various amount of Si in excess deformed after solution heated were investigated by micro-Vickers hardness, electrical resistivity and transmission electron microscopy (TEM). In Al–0.4 mass%Mg2Si alloys containing various amounts of Si in excess, the aging after deformation causes increased maximum hardness (Hmax) for all specimens. The age-hardenability (ΔH) of specimens increases by the deformation of 1% and becomes decreased by further deformation. The aging time to reach maximum hardness, tmax, becomes shortened by the deformation. The distribution and size of precipitates in the deformed specimens are denser and finer than those in specimens without any deformation. In Al–0.6 mass%Mg2Si alloys containing Si up to 0.1 mass% in excess, the aging after deformation causes increased Hmax and ΔH. While, in Al–0.6 mass%Mg2Si alloys containing Si of 0.2 to 0.4 mass% in excess, the values of Hmax remain constant with increasing amount of deformation and the values of ΔH decrease with increasing deformation over 5%. In Al–0.8 mass%Mg2Si and Al–1.0 mass%Mg2Si alloys containing Si in excess, the deformation prior to aging has no effect on Hmax, ΔH and tmax. The precipitates are finer in the alloys which exibit increased ΔH by a small amount of deformation than those of the undeformed alloys. On the contrary, the precipitates are coarsened in the alloys with decreased ΔH by deformation. A small amount of deformation causes decreased values of ΔH at 473 K and increased ΔH at 523 K in the Al–0.6 mass%Mg2Si–0.4 mass%Si alloy. In the Al–0.4 mass%Mg2Si–0.4 mass%Si alloy, however, a small amount of deformation causes increased ΔH at 473 K and decreased ΔH at 423 K.