Pre-strain dependent relaxation behaviour of AA6016 during automotive paint drying processes

Heat treatable aluminium alloys are widely used in modern car bodies to achieve lightweight cars. Compared to steel, aluminium alloys are more sensitive to creep behaviour under high elastic stresses, since their melting point of about 600 °C is much lower. In order to predict permanent deformations of outer shell panels due to thermal stresses in drying processes and ensure highest quality standards regarding appearance to the customer, interdependencies with production process history must be evaluated. In this work, stress relaxation of the aluminium alloy AA6016 in initially T4 temper has been examined within the elastic regime with focus on the dependency of plastic pre-strain during primary creep phase. As a result, pre-strain becomes more important the higher the temperature was set. Hence, the former production process history of aluminium sheet metal parts must be taken into account when viscoelastic deformations are investigated. Based on the test results a pre-strain dependent material model for finite element simulations is pointed out, which can be used for novel deformation analyses of car bodies in automotive paint drying processes that contain aluminium parts out of AA6016.