Influence Of Sc Addition On The Deformed Microstructure, Mechanical Properties And Recrystallization Behavior Of An Al–7Mg Alloy Processed By Hard–plate Rolling

As the most widely used light metallic structural metarial,aluminum alloys have been significant attention in aviation,aerospace and automotive,it is important for industry to achieve more lighter in structure.Aluminum alloy show good shrength and ductility after plastic deformation processed,such as rolling or extrusion.Numerous scholars have researched aluminum alloys deformation behavior during deforming,especially through the severe plastic deformation processing method to prepare aluminum alloys with high mechanical properties,but for difficult–to–deform alloys,its poor formability can only be processed at the high temperature or with multi–passes,the processing technology is complicated and the cost is high,which limits the improvement of the mechanical properties of the aluminum alloy.In our previous work,we have developed the HPR technology,which can process difficult–to–deform alloys at room temperature in one pass and improved the formability of the specimen,will be conducive to the further development and application of hard–deformed aluminum alloys in industry..Based on the hard plate rolling technology,the purpose of this study to reveal the microstructure evolution process of the Al–7Mg–xSc alloys during HPR at room temperature and the influence of the microstructure on the mechanical properties,this study also discussed the recrystallization annealing behavior of the Al–7Mg–xSc alloys after HPR.The main conclusions are as follows:?1?The hard–to–deform Al–7Mg alloys were prepared by hard plate rolling technology at room time.The sample exhibited a bimodal grains microstructure composing of coarse grains(d_cg>100?m)and nanosized grains(d_fg²00nm)by Sc element addition.Moreover, the alloy exhibited superior mechanical properties with a simultaneous high strength and ductility at room temperature,e.g.for the HPR Al–7Mg–0.6Sc alloys,the ultimate tensile strength?UTS?of⁵22 MPa,yield strength?YS?of³19.8 MPa and the elongation of¹9%.?2?It revealed the microstructure evolution of the Al–7Mg–xSc alloys with different Sccontent,which were processed by HPR technology.The Al₃Sc nano–precipitates promote the bimodal microstructure formation during HPR at room temperature,which block the dislocation to increase the local dislocation density,which was beneficial to form the fine grains in the bimodal microstructure by improving the evolution of substructure and dynamic recrystallized.?3?According to contribution of the Al–7Mg–xSc alloys strength from solid solution strengthening,dislocation strengthening,grain boundary strengthening and precipitates strengthening estimated by simplified model,it reveal the influence of the miscrostructure on the mechanical properties at room temperature.Moreover,the work–hardening of the Al–7Mg–xSc were analyzed,the rapidly declines of the work hardening rate of the Al–7Mg alloys before fracture failure was be inhibited,because that the Al₃Sc precipitates improve the dislocation distribution of the microstructure?4?With the 550?/3 h homogeneous,the recrystallization of the Al–7Mg–0.2Sc alloys was earlier occurred during annealing at 350? and 400? compare the Al–7Mg alloys.However,the annealed Al–7Mg–0.2Sc alloys exhibited higher mechanical properties than the same condition Al–7Mg alloys,e.g.the 400?/5 min annealed Al–7Mg–0.2Sc,the UTS³75 MPa and the elongation⁴7%.?5?With the 350?/24 h homogeneous,the size of the Al₃Sc nano–precipitates decrease from 40⁶0 nm to 10²0 nm,and the precipitates were distubuted uniformly in matrix.The microstructure evolution was mainly be effected by precipitates density during annealing at 300?,for the Al–7Mg–0.2Sc alloy,the Al₃Sc promoted the high angle grain boundaries formation by blocking dislocations movement;For Sc content over 0.4 wt.%,the precipitates spacing was small to prevent subgrain boundaries absorption dislocations from forming high angle grain boundaries,it effectively inhibited the recrystallization of the Al–7Mg–xSc alloys.