Effect of pre-deformation on precipitation behavior of AZ80 alloy: Comparison of slip- and twinning-dominant deformation
Hyun Ji Kim, Sang Cheol Jin, Sumi Jo, Sung Hyuk Park
Abstract
• Effect of slip- and twinning-dominant deformation on precipitation of AZ80 was compared. • The internal strain energy of twinning-induced sample is higher than that of slip-induced one. • Twinning-dominant deformation more effectively accelerates precipitation behavior. • {10–12} twins lead to the formation of fine CPs within them and inhibit the growth of DPs. • Twinning-induced sample has a mcuh smaller DP fraction than slip-induced one during aging. This study investigates the effect of the deformation mode on the precipitation behavior of an extruded Mg–8.0Al–0.5Zn–0.2Mn (AZ80) alloy. The alloy samples are compared after the application of 3.5% tension and 3.5% compression along the extrusion direction to induce slip-dominant and twinning-dominant deformation modes, respectively. The pre-compressed (PC) sample, which contained numerous {10–12} tension twins, has a reduced grain size and a higher internal strain than the pre-tensioned (PT) sample, which is attributed to the inherent internal strain that occurs during the formation and growth of the twins. As a result, the precipitation behavior of the PC sample is accelerated, leading to its short peak aging time of 32 h, which is lower than those of the PT and as-extruded samples (48 and 100 h, respectively). Furthermore, fine continuous precipitates (CPs) rapidly form within the {10–12} twins, contributing to the enhanced hardness. Discontinuous precipitates (DPs), which have a hardness comparable to the CP-containing twinned regions, in the PC sample experience less coarsening during aging than those in the PT sample due to growth inhibition by the {10–12} twins. Ultimately, the {10–12} twins generated under the twinning-dominant deformation condition lead to enhanced precipitation behaviors, including the preferential formation and refinement of CPs and the suppressed coarsening of DPs. Consequently, pre-deformation that occurs {10–12} twinning exhibits more pronounced effects on precipitation acceleration and microstructural modification than slip-inducing pre-deformation.