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a b s t r a c tAn FE model of the solution heat treatment, forming and in-die quenching (HFQ) process was developed. Good correlation with a deviation of less than 5% was achieved between the thickness distribution of the simulated and experimentally formed parts, verifying the model. Subsequently, the model was able to provide a more detailed understanding of the HFQ process, and was used to study the effects of forming temperature and speed on the thickness distribution of the HFQ formed part. It was found that a higher forming speed is beneficial for HFQ forming, as it led to less thinning and improved thickness homogeneity.

This paper presents a novel plane-stress continuum damage mechanics (CDM) model for the prediction of the different shapes of forming limit diagrams (FLCs) for aluminium alloys under hot stamping conditions. Firstly, a set of uniaxial viscoplastic damage constitutive equations is determined from tensile experimental data of AA5754 at a temperature range of 350-550 C and strain rates of 0.1, 1.0 and 10 s À1 . The tests were carried out on Gleeble materials simulator (3800). Based on the analysis of features of FLCs for different materials forming at different temperatures, a plane-stress damage equation is proposed to take account the failure of materials at different stress-state sheet metal forming conditions. In this way, a set of multiaxial viscoplastic damage constitutive equations is formulated. The model is calibrated from the FLC data at temperature of 350 C and strain rate of 1.0 s À1 for AA5754. A good agreement has been achieved between the experimental and numerical data. The effect of the maximum principal stress, effective stress and hydrostatic stress on the materials failure features and on the shape of FLCs is studied individually and in combination. Using the newly developed plane-stress unified viscoplastic damage constitutive equations, the FLC of materials can be predicted at different temperatures and strain rate forming conditions.

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A set of unified constitutive equations is presented that predict the asymmetric tension and compression creep behaviour and recently observed double primary creep of pre - stretched/naturally aged aluminium - cooper - lithium alloy AA2050 - T34. The evolution of the primary micro - and macro - variables related to the precipitation hardening and creep deformation of the alloy during creep age forming (CAF) are analysed and modelled. E quations for the yield strength evolution of the alloy, including an initial reversi on and subsequent strengthening, ar e proposed based on a theory of concurrent dissolution, re - nucleation and growth of precipitates during artificial ageing . We present new observations of so - called double primary creep during the CAF process . This phenomenon is then predicted by introducing effects of interact ing microstructures , including evolving precipitates, diffusing solutes and dislocations , into the sinh - law creep model. In addition, concepts of threshold creep stress ??? ??? ??? and a microstructu re - dependant creep variable H , which behave differently under different external stress directions, are proposed and incorporat ed into the creep model . This enables predict ion of the asymmetric tension and compression creep - ageing behaviour of the alloy. Q uanti tative transmission electron microscopy (TEM) and related small - angle X - ray scattering (SAXS) analysis ha ve been carried out for selected creep - aged samples to assist the development and calibration of the constitutive model. A good agreement has been achieved between the experimental results and the model. The model has the potential to be applied to creep age form ing of other heat - treatable aluminium alloys