Plastic Deformation Behavior Of GW83 Magnesium Alloy With Gradient Structure

The low toughness and strength of magnesium alloy have been one of the key reasons to limit its application.Over the past 20 years,related research to improve the strength and ductility of magnesium has achieved great progress.By alloying,texture optimization and grain refinement,the mechanical properties of magnesium have improved a lot.Given its hexagonal close-packed crystal structure,magnesium alloys have a strong deformation anisotropy.Therefore,the homogeneity of microstructure of magnesium alloys plays an important role in intergranular deformation and also the fracture behavior.Correlation of grain size and grain size gradient between deformation behavior of magnesium alloys is consequently of great importance.In this research,by means of Friction Stir Processing(FSP)and annealing,samples of Mg-8%Gd-3%Y(wt.%)(GW83)magnesium alloy with similar texture while different grain size and grain size distribution were processed.By SEM,EBSD assisted with DIC technique,plastic deformation behavior,especially the correlation of grain size as well as its distribution between intergranular deformation compatibility and macro deformation behavior were discussed,the main conclusion was as follows:By controlling the process of FSP and annealing,samples of coarse grain,fine grain as well as gradient structure were acquired.The grain size of fine grain sample is 8?m and that of coarse grain sample is 80?m.Besides,bilayer structure with a more narrow gradient layer is of 85.91% fine grain;bilayer structure with a wider gradient layer is of 81.97% fine grain;trilayer gradient structure is of 80.75% fine grain.In addition,similar texture also the Schmid factor distribution of basal <a> slip,prismatic <a> slip and pyramidal <c+a> slip were analyzed in those two kinds of samples with 100% fine grain and 100% coarse grain.The statistic result of slip traces showed that: samples of fine grain and coarse grain have similar deformation mode where basal <a> slip dominates the tensile deformation at room temperature.Moreover,the misorientation of coarse grain sample slightly decreased after grain refinement.The mechanical property was studied of the samples mentioned above by carrying out the uniaxial tensile experiment at room temperature.The elongation of the five samples are: 14.6%,16.01%,23.7%,26.89% and 28%.The strength of the five samples is of little difference.The results showed that: grain refinement as well as gradient structure can do good to its ductility of GW83 magnesium alloy.Microstructure of deformed fine grain sample and coarse grain sample was observed and studied at the same tensile strain by in-situ SEM,in-situ-EBSD and DIC technique.Influence of gradient structure on intragranular/ intergranular deformation mode as well as deformation behavior was discussed.The result showed that: 69.5% of grain pairs occurred slip transfer in fine grain samples whereas 40% of grain pairs occurred slip transfer in coarse grain samples,which suggests that the increase in elongation of fine grain sample compared to coarse grain one is owned to the higher fraction of activated slip transfer,therefore,more strain can be accommodated.Moreover,DIC result also showed that: fine grain zone accommodated more strain by 34.1% compared to coarse grain zone in the same sample.Moreover,strain concentration can be observed in coarse grain zone while strain distribution of fine grain zone is more uniform.Due to the similar Schmid factor distribution and intragranular deformation mode,the fraction difference of activated slip transfer of fine grain and coarse grain sample results from different grain misorientation.It is demonstrated that m' factors between the adjacent two grains where slip transfer activated are all over 0.5.Fine grain sample with more fraction of activated slip transfer corresponding to higher m' value,consequently accommodates more strain.Therefore,trilayer structure with fine grain zone lying on each side of the sample,which can accommodate more strain,prevent initiation and propagation of micro-cracks,performs a better overall ductility.