Influence of plastic deformation on the precipitation sequence in an AA6061 alloy

Abstract

The purpose of this work is to study the effect of prior plastic deformation on the precipitation mechanisms of MgxSiy in an AA6061 alloy. Differential scanning calorimetry (DSC), tensile testing and transmission electron microscopy (TEM) were used to characterize the precipitation sequence in samples that were isothermally aged at 180 °C with and without prior plastic deformation. Compressively deforming the AA6061 alloy by 4% caused a shift in the exothermal precipitation peaks to lower temperatures (DSC) and enabled the peak strength condition to be reached after a shorter aging period, revealing that plastic deformation accelerated the precipitation kinetics. TEM analysis determined that the accelerated precipitation kinetics in the deformed material was due to heterogeneous precipitation of the Q′ phase along dislocation lines and a modification of the precipitation sequence with the L, C and Q′ phases dominating over the β′′ phase (which is dominated in the non-deformed material). Additionally, the formation of β′ was largely suppressed by plastic deformation.