Investigation On The Deformation Behavior Of AT63Magnesium Alloy At Room And Elevated Temperatures

In recent years, people have paid more and more attention to the magnesium alloyscontaining Sn. Mg2Sn phase can be formed by adding Sn element, and thus significantlyimproves the creep resistance and strength of magnesium alloy because of its high meltingpoint, hardness and thermal stability. Moreover, non-basal slip activates more easily due tothe the decrease of stacking fault energy by the addition of Al and Sn simultaneously, andthus improving the ductility of magnesium alloy. Therefore, further study on wroughtmagnesium alloy with Sn element has the vital significance to the development of new typesof high ductility and strength magnesium alloy.In this study, the mechanical property tests and microstructure characterization ofMg–6Al–3Sn (AT63) magnesium alloy were carried out at room temperature and hightemperatures, researches are focused on the deformation anisotropy and strain rate sensitivity(SRS) at room temperature and dynamic recrystallization and grain boundary sliding atelevated temperatures, in addition, the deformation mechanisms of AT63magnesium alloyare discussed. Therefore, we draw the following conclusions:(1) The extruded AT63alloy with distribution of basal poles towards the transversedirection (TD) shows obvious in-plane anisotropy during tensile deformation. ED sampleexhibits higher yield stress (208MPa) while TD and45D sample exhibit equal value (153MPa). ED sample has the highest tensile strength (296MPa) and the lowest elongation tofailure (19.8%), however,45D sample has the highest elongation to failure (30.9%) and thelowest tensile strength (276MPa). For the work hardening exponent: TD sample>45Dsample> ED sample.(2) The compression behavior of extruded AT63alloy is strain rate sensitive. As thestrain rate from10–4s–1increases to10–1s–1, the fracture strain of three directions (ED, TDand ND) increases from11.6%,12.8%and9.6%to12.8%,16.8%and12.3%, respectively.However, the yield strength and ultimate compressive strength for ED decreases from116 and416MPa to106and410MPa, while decreases from116and398MPa to100and370MPa for TD. For ND, the yield strength increases from123MPa to140MPa, and theultimate compressive strength decreases from350MPa to339MPa.(3) Twinning has a significant effect on tensile deformation behavior of extruded AT63alloy at room temperature.{1012} twinning nucleation occurred at an early deformationstage (ε<2.5%) when tension along TD and45D, while lasted until a later deformation stagewhen tension along ED. In addition, different {1012} twin variants formed leads to twinboundary showing the intersection morphology in the TD but lamellar morphology in the45D. A great quantity of crossed twin boundaries blocking the dislocation slip increases thework hardening ability of the TD, and the parallel twin boundary promoting the dislocationslip improves the plasticity of the45D.(4) The SRS of the extruded AT63alloy exhibits obvious anisotropy due to thedifferent activated deformation modes. When compressed along ED, the activated twinningmode transformed from {1012} to {1011} twinning results that the negative SRS increasesat low strains (ε<7%) and then decreases at high strains (ε>7%). When compressed along TD,the SRS remains almost the same (i.e. closing to-0.014) at all strains, which is attributed tothe coexisting of {1012} and {1011} twins. When compressed along ND, the SRS showspositive at low strains (ε<4%) for pyramidal <c+a> slip-dominated and then decreases tonegative at high strains (ε>4%) due to activation of {1011} twinning.(5) Deformation temperature has an important effect on the deformation behavior ofrolled AT63alloy at elevated temperatures. The rolled AT63alloy appears superplasticitywhen tensile temperature increased to200oC. Dynamic recrystallization occured earlier athigher deformation temperature, when the deformation temperature is250oC, dynamicrecrystallization already completed before fracture, but when150oC, it is not completedeven at fracture. In addition, grain rotation as the main coordination mechanism for grainboundary sliding occurred at250oC, therefore, rolled AT63alloy obtained a high plasticity.