Effect of large cold deformation after solution treatment on precipitation characteristic and deformation strengthening of 2024 and 7A04 aluminum alloys

Abstract

The effects of large cold deformation after solution treatment on the precipitation characteristic and deformation strength of 2024 and 7A04 Al alloys were investigated. The tensile property tests indicate that the ageing response of the 2024 aluminum alloy is accelerated when treated by cold deformation after solution treatment, and the tensile strength is increased to about 140 MPa while the elongation still keeps above 8%. However, compared with the 2024 alloys, although the aging response of the cold deformed 7A04 aluminum alloy is accelerated, the tensile strength has not changed obviously and the elongation is even decreased drastically. The results of TEM observation show that the S' phase inside the dislocation cells and at the boundaries of the dislocation cells of the 2024 aluminum alloy has a uniform distribution. But in 7A04 aluminum alloy the club-shaped η' phase forms at the boundaries of dislocation cells even on dislocation lines, while there still exists small spheric G.P zone in the region with less dislocation. In addition the precipitates in 7A04 alloy with cold rolling present more obvious tendency of growth and coarsening than those without cold rolling. It is indicated that the coherent strain energy of the cylinder formed G.P zones with matrix in the 2024 alloy is smaller than that of the spherical G.P zone in 7A04 alloy, for which a different distribution of precipitates and different effect of strengthening are caused in artificial ageing after resolution treatment and large cold deformation.