Understanding the isothermal compression behavior of Al-Mg-Si alloy based on hot deformation parameters and instability criteria

This work comprehensively studied the microstructure evolution and thermodynamic behavior of homogenized cast Al-Mg-Si alloy by using the dynamic materials model (DMM) of hot deformation activation energy (Q) and power dissipation efficiency (η), which were influenced by Zener-Holomon (Z) parameters of temperature-compensated strain rate. The Q varies with the material constitutive parameters n(T) and sε̇ and leads to a non-monotonic trend in the Z parameter. These coupling relationships have profound significance for revealing plastic deformation. The microstructure and microtexture evolution under four representatively Z parameters had been characterized, and it was found that the deformation mechanism under higher lnZ was mainly dynamic recovery (DRV) and a typical <101>//TD texture with a maximum strength of 14.41 was exhibited. As lnZ decreased, the volume fraction of high angle grain boundaries (HAGBs) and recrystallized grains increased from 20.89 % and 1.5 % to 49.47 % and 40.9 %, the geometrically necessary dislocation (GNDs) density dropped from 1.55 × 10¹⁴/m² to 0.40 × 10¹⁴/m², and the softening mechanism gradually shifted to dynamic recrystallization (DRX), with the volume fraction of Cube texture {001} <100> increasing and Goss texture {011} <110> decreasing. Hot processing maps were established based on the Prasad and Murty instability criterion. The results showed that the instable and stable zones had a strong correlation with η. Lower η often implies microcracks, deformation bands and flow localization, as well as extremely uneven grain distribution and a low recrystallization volume fraction, and the stable zone mainly exhibited the phenomenon of DRX dominated recrystallization behavior improving microstructure homogenization. By comparing the specific hot processing map and microstructure evolution, the prediction ability for determining Murty instability criterion is stronger than Prasad for homogenized cast Al-Mg-Si alloy.