Effect Of Rolling Process On The Recrystallization Microstructures And Mechanical Properties For The As-casting AZ31Mg Alloy Sheets

The continuous cast-rolling forming technology of deformation magnesium alloys wasa new forming process method. There were some advantages about it as a short process, saveenergy and reduce costs, etc. In recent years, the engineering and academic researchers had aresearch focus on it at home and abroad. However, it needed to optimize the rolling processduring the next rolling process, in order to produce both surface and internal quality toachieve the requirements for preparation of sheets and other products. Especiallyhigh-performance magnesium alloy sheets had great prospects. The continuous cast-rollingforming technology was one of the main ways to get thin magnesium alloy sheets, a largenumber of industrialized production of magnesium alloys sheets had far-reachingsignificance and great practical interest. However, magnesium alloy has a close-packedhexagonal crystal structure, less slip systems, poor plastic deformation and poor anisotropyseverely, which greatly limits the industrial applications of magnesium alloys sheets. Tosolve this problem, we further optimize the rolling process AZ31cast-rolling magnesiumalloys sheets. At present, the different speed ratios and rolling directions of the rollingprocess is not particularly systematic research. In this study, we aimed to examine the effectof small speed ratios and rolling directions on the recrystallization microstructures, texturesand mechanical properties of the casting-rolling AZ31Mg alloy sheets at room and elevatedtemperatures, and some results are as follows:(1) At room temperature, the recrystallization texture had been weakened with the smallspeed ratios increasing, but the changes were not very significant. The texture strengthof slow speed roll side was higher than rapid speed roll side. Differential speed rollingcaused dynamic recrystallization and short time annealing during the passes resulted inthe occurrence of static recrystallization, which made the grain orientationredistribution, leading to weakening of texture. At the speed ratio of1.2, differentialspeed rolling refined the organizations more effectively.(2) At room temperature, with different speed ratios increasing, the tensile strength reduced from245MPa to234MPa. When the speed ratio was1.2, the tensile strength and yieldstrength of240MPa and145MPa, the maximum plastic elongation achieved25.6%,and compared to the speed ratio of1.0, the plastic elongation improved5.7%, due tograin refinement and weakening texture interaction.(3) At elevated temperature, as the deformation temperatures and the speed ratios increasing,the plastic elongation gradually increased. And the maximum plastic elongation was86.3%at250oC. In summary, the optimum rolling process was the speed ratio of1.2,and the room temperature and elevated temperature plastic elongation were25.6%and86.3%.(4) Rolling direction had a significant effect on the grain size of rolled AZ31magnesiumalloy, and the grain distribution was relatively uniform. As changing the rollingdirections, the recrystallization texture had been significantly enhanced, especially thestrongest cross-rolling texture intensity, mainly due to the rolling directions changes.(5) At room temperature, the head and tail rolling had the best mechanical properties, withthe tensile strength of295MPa, the yield strength of196MPa, the elongation-to-failureof31.5%and the plastic elongation of29.4%respectively. The specimen of the clockrolling had excellent integrated mechanical properties at200oC, theelongation-to-failure came to the maximum of97.2%, and the tensile strength was94MPa. In summary, the optimum rolling process was the head and tail rolling (roomtemperature) and the clock rolling (elevated temperature).