A parameterization method of recovery behavior based on initial yield stress - pre-strain diagram for an Al-Si-Cu high pressure die-casting alloy

Consideration of recovery behavior in the constitutive equation of alloy is crucially important for accurate thermal stress analysis of the casting process. However, previously reported empirical equations present difficulties when including a coefficient that determines the ratio of the recovery (or strain-hardening) strain component because the alloy recovery behavior has not been investigated systematically. First, this study systematically revealed effects of the temperature and amount of inelastic strain at 200-440 °C on the increase of the initial yield stress of the room temperature (RT) in an Al-Si-Cu high-pressure die casting alloy. Secondly, from those results, an initial yield stress - pre-strain diagram was proposed, demonstrating the effect of the amount of the inelastic strain given at each temperature on the increase of the initial yield stress of RT. Finally, this study newly defined a temperature-dependent contribution ratio of strain hardening to parameterize and duplicate the alloy recovery behavior based on the initial yield stress - pre-strain diagram for the constitutive equation of the alloy. Using this ratio as the coefficient to determine the proportion of the strain contributing the strain hardening for the constitutive equation, thermal stress analysis can produce more accurate duplication of the experimentally determined recovery behavior. Thereby, the residual stress and deformation of the component in the casting process can be predicted more accurately than when using conventional empirical constitutive equations.