Experimental studies and constitutive modelling of the hardening of aluminium alloy 7055 under creep age forming conditions

Abstract

A test programme has been designed to characterise the creep-ageing behaviour of Aluminium Alloy 7055, commonly termed AA7055, under creep age forming (CAF) conditions. Creep ageing tests have been carried out for a range of stress levels at 120 °C for 20 h, which is the typical period for a CAF process. Interrupted creep tests have also been carried out to rationalise the effect of stress levels on age hardening. Based on experimental observations, a set of mechanism-based unified creep ageing constitutive equations has been formulated, which models creep induced evolution of precipitates, dislocation hardening, solid solution hardening and age-precipitation hardening. A multiple-step reverse process has been introduced to determine, from creep ageing test data, the values of constants arising in the constitutive equations. Close agreement between experimental data and computed results are obtained for creep and age hardening data for the stress range tested. The determined equation set has been integrated with the commercial FE code MSC.MARC via the user defined subroutine, CRPLAW, for CAF process modelling. In addition to springback, the evolution of precipitate size and creep induced precipitation hardening can be predicted.