Modelling the effect of cooling rate on tensile properties of 6xxx series aluminium alloys for automotive applicationsWednesday (08.11.2017) 17:20 - 17:40 Part of:
During processing of age-hardening 6xxx series aluminium alloys for automotive applications, the sheets may experience significant variations in the cooling rate following the solution heat treatment at the aluminium supplier prior to the final paint bake cycle at the carmaker. Certain 6xxx series aluminium alloys are known to be susceptible to slow cooling following the solution heat treatment, a phenomena known as quench-sensitivity. Quench sensitive aluminium alloys usually contain a high density of dispersoids that form during the homogenisation cycle. The dispersoids may have a negative effect on the resulting yield strength since coarse non-hardening beta’ type of particles may nucleate at the dispersoids during cooling and reduce the solid solution concentrations of Mg and Si and thus the hardening potential of the alloy. In the present study we explore the impact of various cooling rates on the resulting tensile properties for three different 6xxx series aluminium alloys with a wide variation in the number density and size of the dispersoids as quantified by Scanning Electron Microscopy (SEM). A combined precipitation, yield strength and work hardening model called NaMo was used to calculate the nucleation and growth of coarse non-hardening beta’-particles during cooling as well as the subsequent precipitation of hardening beta’’-particles during a final artificial ageing heat treatment. Based on dislocation theory, the resulting yield strength and work hardening of the alloys were predicted and compared with tensile tests conducted on the actual alloys. The results revealed a good correlation between model simulations and measurements, and thus encourage the use of the NaMo model in future process and alloy development.
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|Short Paper||Modelling-Quench Sensitivity-6xxx-alloys||Short paper||647 KB||Download|