Investigation On The Tension-Compression Asymmetry And Deformation Mechanism Of The Cast Mg-10gd-3y-0.5zr (wt.%) Alloy

Age-strengthened rare-earth（RE）magnesium（Mg）alloys often have a good age-strengthening,which is generally considered to be related to the relatively good barrier effect of prismatic precipitation.However,the influence of prismatic precipitation on the relative activity of each slip mode is controversial and lacks quantitative experimental research.And there are few studies on the mechanical properties of aged heat treatment showing different strengthening effects under tensile and compressive loading.As an age-strengthened Mg alloy,Mg-10Gd-3Y-0.5Zr（wt.%,GW103）alloy has excellent properties such as high strength and good creep resistance.However,for this alloy under different loading conditions at room temperature,the deformation behavior and the influence of the precipitates need to be further studied.In conclusion,the research on the mechanical behavior and deformation mechanism of GW103 Mg alloy under different loading conditions/aged states is needed.In this paper,the cast GW103 Mg alloys in different heat treatment states（solid solution state,T4;peak-aged state,T6）were used as materials,and characterized by scanning electron microscope（SEM）and electron backscatter diffraction（EBSD）,based on mechanical behavior analysis,quasi-in-situ slip trace analysis and EBSD misorientation analysis,respectively.Under different loading conditions（tensile and compressive）,the effect of aged heat treatment on the alloy was studied from three aspects macroscopic mechanical behavior（strength and strain-hardening rate）,deformation mechanism（slip）and plastic heterogeneity（intragranular misorientation angle,kernel average misorientation and geometrically necessary dislocation density）,respectively.The main conclusions are summarized as follows:（1）For GW103 Mg alloy during tensile and compressive loading deformation,the effect of aged heat treatment on the mechanical properties was quite different（the yield strength in the tensile process was significantly affected）.At 1%strain,after aged heat treatment,the deformation characteristics of the alloy were significantly weakened during tensile deformation,while there were more abundant deformation characteristics during compression deformation.The specific performance was as follows:（a）regardless of tensile or compressive deformation,aged heat treatment inhibited the grain with slip trace,and the inhibition effect was stronger during tensile deformation.（b）After aged heat treatment,the grain with multiple slip was inhibited during tensile deformation,which promotes multiple slip during compression deformation.（c）After aged treatment,it was very difficult to find grain with cross slip during tensile deformation,while compression deformation promoted cross slip.When the strain increased to 5%,the existing deformation characteristics were more obvious,and there was no other obvious change.（2）The results of slip trace analysis showed that（the number of grains analyzed for each sample exceeds 200）:（a）at 1%strain,after aged heat treatment,the dominant slip mode was changed from the basal<a>slip to prismatic<a>slip,and its relative frequency change as follows:basal<a>slip decreased from 60%to 29%during tensive deformation,and from 59%to 19%during compression deformation;prismatic<a>slip increased from 10%to 41%during tensive deformation,and from 9%to 33%during compression deformation.（b）When the strain increased to 5%,the relative activation frequency of each slip mode did not change much,and the arrangement order did not change.（c）The distribution law of Schmid factor of each sample was roughly the same.After aged heat treatment,the degree to which non-basal slip did not obey Schmid law diminishes;there were always some hard-oriented（m≤0.1）slip modes activated.（d）For the normalized Schmid factor,the aged treatment increased the non-basal slip frequency of m_nor>0.4,there was also non-basal slip of m_nor<0.1.（3）Most grains with multiple slip only had two slip systems.During compression deformation,the grain with cross slip was more likely to occur,and the mainly cross slip with the participation of basal<a>slip.For slip transfer:（a）aged heat treatment inhibited the occurrence of slip transfer,and the frequency of grains with slip transfer was always higher during compression deformation.（b）Among the samples,the slip mode most prone to slip transfer was significantly different.（c）When the strain is increased to 5%,the general law of slip transfer was similar to 1%strain.（d）The normalized geometric compatibility factor(m’_nor)and Schmid factor(m_nor)were used together to better evaluate slip transfer,most slip transfers showed the following rules:when m’_nor was small（<0.6）,m_nor had at least one larger value（>0.4）;when m_nor was small（≤0.1）,m’_nor was a larger value（>0.6）.（e）For the grain boundary where slip transfer occured,the grain boundary misorientation angle（GBMA）tended to have a preferential distribution.The grain boundary in a specific GBMA interval（such as 10°～20°）was more prone to slip transfer.（4）Aged heat treatment can reduce the increase of plastic heterogeneity,and the places with large plastic heterogeneity were mainly distributed near the grain boundary.The magnitude of plastic heterogeneity had no obvious relationship with the spatial location of the slip trace.For regions where most grain boundaries exhibited extremely large geometrically necessary dislocation densities,it satisfies at least one of the following conditions:（a）large GBMA（≥60°）;（b）for specific slip modes between adjacent grains,there was a large difference in its maximum Schmid factor（>0.1）.