Microstructure analysis of an Al-Zn-Mg alloy during porthole die extrusion based on modeling of constitutive equation and dynamic recrystallization

Abstract In this study, the dynamic recrystallization (DRX) behavior of an Al-Zn-Mg alloy during porthole die extrusion process was studied. Firstly, the hot compression tests were conducted at varied temperatures and strain rates. The constitutive equation was established based on modified Arrhenius and Johnson-Cook models, respectively, and DRX kinetic equation was established based on modified Avrami model. Secondly, transient simulation using the established constitutive and DRX kinetic equations was performed for porthole die extrusion process. Finally, in order to verify the accuracy of simulated results, the extrusion experiment was conducted and the microstructure was analyzed. The results show that both the strain compensated Arrhenius model and modified Johnson-Cook model can accurately describe the flow stress of Al-Zn-Mg alloy at elevated temperature. Higher deformation temperature and lower strain rate are favorable for the occurrence of DRX. The volume fraction of DRX at the zones close to bridge and porthole wall is much higher than that in the other zones, and this kind of inhomogeneous DRX behavior is mainly attributed to varying distribution of stain. According to the experimental results, several subzones with different microstructures were identified. Importantly, the simulated DRX volume fraction shows good agreement with the experimental results.

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