Influence Of Grain Size And Strain Rate On The Deformation Behavior Of Rolled AT33Alloy At Room And Elevated Temperatures

Wrough Mg alloys have wide applications in automobiles, aerospace and other fieldsdue to their excellent mechanical properties. However, the industrial application of wroughMg alloys has been greatly limited due to there hexagonal close-packed (hcp) structure.Consequetly, it has become a hot and difficult problem to improve the deformation ability ofMg alloys.Recently, the effects of Sn addition on the deformation behavior of Mg alloys haveattracted people’s attention. Firstly, the decrease of stacking fault energy (SFE) caused bysimultaneous Al and Sn dopings can promote the activation of the non-basal slips, and thusimproving the ability of plastic deformation; In addition, the Mg2Sn particles with highmelting point and hardness can significantly improve the strength and creep resistance of Mgalloys. Cosequently, delving into the deformation behavior of Mg–Al–Sn alloys is of greatimportance to develop new high performance magnesium alloys.In this study, we aim to examine the influence of grain size and strain rate on thedeformation behavior of rolled Mg–3Al–3Sn (AT33) alloy at room and elevatedtemperatures，and some results are as follows:(1) The deformation mechanisms for rolled AT33alloys were strongly dependent ongrain sizes at room temperature. For grain sizes of~6–22m, the deformation in tension wasmainly dominated by dislocation-slip, which, however, turned to be mediated bydeformation-twinning for those of~22–41m. Moreover, as deformation proceeded,Hall–Petch slopes for slip-controlled-plasticity (kS) decreased gradually due to continuousactivation of non-basal slips, while that for twinning-mediated-plasticity (kT) increasedrapidly owing to increase in twin number and density, corresponding to grains below andabove the medium-size of~22m respectively. (2) The strain rate sensitivity (SRS) for rolled AT33alloys increased with decreasinggrain size at room temperature, owing to transformations in deformation mechanisms fromdislocation-dominated to twinning-mediated deformation. Moreover, as deformationproceeds, the SRS for slip-dominated grains (~6m) decreased gradually due to continuousactivation of <c+a> slip, while that for twinning-mediated grains (~41m) decreasedrapidly because of the combined action of <c+a> slip, contraction twinning ({1011}1012)and extension twinning ({1012}1011).(3) The strain rate played an important role in the deformation behavior of rolled AT33alloys at elevated temperatures. The deformation behavior satisfied the hyperbolic sineconstitutive equation:2.641012[sinh(0.01)6.5]exp[145000p。The activation energy (Q)RT]value and average stress exponent (n) is145kJ/mol and6.5, respectively, indicating that thedeformation mechanisms at elevated temperatures is climb-controlled creep. In addition,when tensioned at a strain rate of10–1s–1, the increase of n-value with increasing deformationtemperature (from RT to100oC) was preliminary attributed to the enhancement of an foresthardening mechanism, while the decrease of n-value with the further increasing ofdeformation temperature (100–250oC) was the results of the combined action of dislocationclimb and cross-slip, as well as the dynamic recrystallization.(4) The grain size also played an important role in the deformation behavior of rolledAT33alloys at elevated temperatures. With increasing temperature, the disparity of peakstrength between the small-grained (~7m) and large-grained (~41m) samples dereasedgradually, but the disparity of elongation-to-failure incrased obviously. In addition, thegradually decreasing of n-value of the both samples with increasing deformation temperature(from RT to100oC) was mainly attributed to the dislocation climb and cross-slip and adecreasing of the forest hardening mechanism. However, with the further increasing ofdeformation temperature (100–250oC), the n-value of small-grained decreased rapidly dueto the action of dynamic recrystallization, while that for large-grained (~41m) samplesdecreased gradually because of the combined action of the dislocation climb and cross-slipand a decreasing of the forest hardening mechanism.