Effects of asymmetric creep-ageing behaviour on springback of AA2050-T34 after creep age forming

Abstract

Abstract This study investigates the effects of asymmetric creep-ageing behaviour on springback of aluminium alloys during creep age forming (CAF) process. An Al-Cu-Li alloy, AA2050, which shows an apparent asymmetric tension and compression creep-ageing behaviour is used for investigation. Several CAF trial tests to form singly-curved AA2050 plates with different thicknesses (3, 5 and 8 mm) are carried out with a four point bending setup. Meanwhile, two sets of finite element (FE) models of corresponding processes have been developed, in which either the conventional symmetric or the new asymmetric creep-ageing behaviour of the alloy was used. The asymmetric models can well predict the shape of formed plates for thicker materials (5 and 8 mm), while symmetric models provide over-prediction of final deflections. The results from asymmetric models indicate that more creep strain is generated in the tension stressed part of the forming plate than that in the other part with compressive stresses and therefore, resulting in an asymmetric distribution of the relaxed stresses through the thickness of the forming plates after creep-ageing. After springback, both top and bottom surfaces of the formed plates show significant compressive stresses while tensile residual stresses exist in the centre of the formed plates. The work in this study helps to understand the particular springback behaviour of AA2050 with asymmetric creep-ageing behaviour in CAF, and can be used to guide future industrial applications of the alloy in the CAF process.