Effect of Aging Time on Multiaxial Plastic Behavior of A2024-T_6 Aluminum Alloy

Multiaxial stress tests were carried out on thin-walled cylindrical specimens of the A2024-T6 aluminum alloys strengthened by two different precipitates. One of the A2024-T6 alloys has the (GP[1]+GPB) structure obtained by aging for 10min at 200°C; the other has the (θ'+S') structure obtained by prolonged aging of 5.5hr at 200°C. The effect of aging time was examined by comparing two types of plastic deformation behavior. From the proportional combined loading tests of axial load, internal pressure and torsion, it was found that the flow stresses changed with a rotation of the principal stress axes and a difference arose between the directions of the principal stress and principal strain increment. Under tension-internal pressure and tension-torsion, the equi-strain surfaces and strain behavior were also determined. Both alloys exhibited axisymmetric anisotropy. The degree of anisotropy was larger in the 2024-T6 (10min) than in the 2024-T6 (5.5hr). In addition, the plastic deformation behavior could be expressed precisely by the constitutive equation derived from the proposed yield function, hardening law and associated flow rule.