Effect of Al3(Sc,Zr) dispersoids on the hot deformation behaviour of 6xxx-series alloys: A physically based constitutive model

The hot deformation behaviour of two model Al-Mg-Si alloys was assessed. One alloy was representative of the 6xxx series containing small additions of Mn and Cr, while the other contained small additions of Sc and Zr. Prior to deformation, a multi-stage heat treatment was conducted on the alloys to solutionize the Mg and Si and promote the precipitation of Al-3(Sc,Zr) dispersoids in the Al-Mg-Si-Sc-Zr alloy. Uniaxial hot compression tests were conducted at various temperatures (683-823 K) and strain rates (1-125 s(-1)) and the resulting flow stressstrain curves were evaluated. Flow stress values were observed to be slightly increased in the alloy containing Sc and Zr. The activation energy for hot deformation and material constants for each alloy were calculated, which in turn provided a good prediction of the experimental data. The post-deformation microstructures were analysed using SEM and TEM. The capacity for dynamic recovery was reduced, while dynamic recrystallization was prevented in the Al-Mg-Si-Sc-Zr alloy. This was a result of restricted dislocation motion, caused by the pinning of dislocations from the Al-3(Sc,Zr) dispersoids. The relative flow stress of the Al-Mg-Si-Sc-Zr alloy was found to compare favourably to other 6xxx series alloys with similar mechanical properties.