Deformation Behavior, Recrystallization Kinetics, Strengthening Mechanisms and Residual Stress in Al-Mg-Si-Ag Alloy Processed by Equal-Channel Angular Pressing

Equal-channel angular pressing was conducted on 6063 aluminum alloy containing a small silver (Ag) addition up to 4 passes at room temperature following route Bc. Mechanical properties assessed by nanoindentation measurements indicated that the Ag affected the plastic deformation mechanism by suppressing grain boundary sliding. Eventually, this led to the occurrence of dynamic recovery following the second pass. The occurrence of dynamic recovery was confirmed by differential scanning calorimetry. X-ray diffraction analysis revealed a steady-state condition of crystallite size, microstrain and dislocation density after the first pass due to the occurrence of dynamic recovery, indicating that the Ag stabilizes the microstructure. Recrystallization kinetics predicted by the Johnson–Mehl–Avrami model, involved two distinct stages being characterized by different Avrami exponent values. Both stages exhibited relatively high activation energy values, revealing that Ag improves the thermal stability. Analysis of contributions of various strengthening mechanisms showed that significant contribution arises from dislocation density and Ag provides additional strengthening. The relatively low magnitudes of residual stress further revealed the role of Ag as stress reliever.