Optimization of hot deformation processing parameters for as-extruded 7005 alloys through the integration of 3D processing maps and FEM numerical simulation

Abstract

The hot deformation behavior and microstructure were investigated for as-extruded 7005 alloys, which is the same as the billet state in real applications in the commercial forging process. It provides a more accurate understanding of the hot deformation flow behavior and microstructure evolution of 7005 alloys for commercial forging processing engineers and mold designers. The compression tests were conducted in temperatures 300–550 °C and strain rates 0.001–1 s−1 using an isothermal hot compression test. The power dissipation efficiency (η) and instability parameter (ξ) were calculated according to the true stress-true strain data obtained from the thermal compression tests. 3D thermal processing maps including the true strains were generated for as-extruded 7005 alloys, and the optimal processing conditions were selected according to η, ξ, and microstructure. The results showed that η increased with increasing temperature but decreased with increasing strain rate. The size of the instability region expanded with decreasing temperature and with increasing strain rate. An η < 0.20 is generally designated an instability region. Microscopic defects such as micro cracks and flow localizations could be observed, and the microstructures of the stability regions showed fine recrystallized grains with η above 0.30. The optimal processing conditions were determined to be a processing temperature between 425 and 500 °C and a strain rate between 0.1 and 0.01 s−1. This study is the first to optimize the closed die forging processing parameters through integration of 3D processing maps and a numerical simulation for a hub based on its real workpiece appearance. A function for prediction of the microstructure evolution is provided using commercial simulation software to help mold designers and forging processing engineers reduce the trial time.