“Modeling Heat Treatment of 7075 Aluminum Components”

Aluminum alloy 7075 is heat treated to improve strength and performance.  Typical heat treatment consists of solution treatment followed by age hardening.  Often, additional metalworking occurs between these heat treatment steps.  A project was recently completed to characterize the solution treatment and age hardening kinetics of 7075 aluminum experimentally, and to develop a capability to model the dimensional change, stress state and metallurgical state of components subjected to these heat treat steps.  An experimental program was developed and conducted at Case Western Reserve University to develop data needed for such a heat treatment model. Using electrical resistivity, hardness and tensile tests, metallurgical data were developed for solution treated, age hardened and over-aged conditions.   Phase transformation kinetics parameters for diffusion-based dissolution and age hardening models were developed from the experimental data, as were data for constitutive and thermal models.  The transformation models and the material data were implemented into an internal state variable material model linked to a commercial finite element solver.  Simplified geometric models were developed to evaluate model performance for the experimental tests.  Then, a production “T” shaped forging was dimensionally characterized before and after heat treatment, and it served as a component for demonstrating the software capabilities.  Comparison of actual and predicted dimensions showed merit to both the modeling method and the experimental procedures used to gather the necessary property data.