The present study investigates the effect of coupled thermo-mechanical phenomena, referred to thermal evolution and plastic deformation, during hot stamping of precipitation hardenable aluminum alloy AA7075 by using an in-situ approach of differential cooling in combination with electron microscopy. To explore the intrinsic geometry-dependent local strain distribution of the tailored microstructure, digital image correlation coupled with tensile tests is used. The precipitates size distribution, morphology and types are investigated using electron channeling contrast imaging and differential scanning calorimetry. Results indicate that the forming tool temperature and contact time within closed forming tools are influential parameters for tailoring the microstructure distribution. A sigmoidal curve-like hardness distribution is found for the forming tool temperature difference of 24 °C–300 °C and 24 °C–350 °C, showing a steep decrease from 180 HV5 to 123 HV5. This is explained by the detected coarse and lath-shaped quench-induced precipitates in the soft zone and formation of fine strengthening η′-phase type in the hard zone in areas with higher supersaturation. Transition zones contain a mixture of precipitates structures of varying morphology and types, with a lower aspect ratio on the heated section. This fact leads to an inhomogeneous plastic deformation mainly located in the heated zones and consequently a high strain hardening rate due to the increased inter-particle-spacing and higher dislocation mean free path. Post-cooling after differential cooling generates higher mechanical properties for water-quench compared to air-cooling, as it prevents the nucleation of quench-induced precipitates and segregation of solute atoms to grain boundaries.      «

The present study investigates the effect of coupled thermo-mechanical phenomena, referred to thermal evolution and plastic deformation, during hot stamping of precipitation hardenable aluminum alloy AA7075 by using an in-situ approach of differential cooling in combination with electron microscopy. To explore the intrinsic geometry-dependent local strain distribution of the tailored microstructure, digital image correlation coupled with tensile tests is used. The precipitates size distribution,...     »