Constitutive modelling of primary creep for age forming an aluminium alloy

The age forming technique has been used in aerospace industry to manufacture panels components with improved mechanical properties and reduced fabrication cost. Age forming is based on the stress relaxation phenomenon due to creep, which occurs during the artificial ageing of a metal. Different from other metal forming techniques, ‘ageing–creep’ deformation takes place well below yield point and the amount of plastic deformation is directly related to ageing time and temperature. The aim of this paper is to model the ageing–creep behaviour of an aluminium alloy in industrial age forming process. Ageing–creep tests are carried out at 150 °C for a solution treated and quenched aluminium alloy. A new set of physically based, unified ageing–creep constitutive equation is developed based on the ‘unified theories’ and ageing kinetics. The material constants within the equations are determined from experimental results and evolutionary algorithm (EA) based optimization package. Close agreement between the predicted and experimental creep curves has been achieved.