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 (H_max) 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, t_max, 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 H_max and ΔH. While, in Al-0.6 mass%Mg₂Si alloys containing Si of 0.2 to 0.4 mass% in excess, the values of H_max remain constant with increasing amount of deformation and the values 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 H_max, ΔH and t_max.,. 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.