Research On Large Reduction Rolling Process And The Deformation Behavior Of AZ31 Magnesium Alloy Sheet

Mg is abundant, due to its high proportion in the earth, which could be foundation for large application in the future. Nowadays depending on its many advantages, Mg alloy was developed so much. Even though, the application of Mg alloy was still restricted. There exist two critical points-low strength and low manufacture efficiency. Manufacture efficiency is concerned in this paper, which efficient rolling process of magnesium alloy sheets is researched in. Enhancing reduction of each rolling pass is adopted as a method to shorten passes and improve efficiency.The reversible rolling mill used in this study is designed by ourselves, especially temperature of the rollers` surfaces can be maintained at 250 ℃ steadily, even during rolling. And it has been proved that this method is particularly good for magnesium alloy to improve the plasticity and relieve edge crack. First, by this method, as-annealed AZ31 sheets were rolled for only one pass at different reduction ratio 10%~60%. The sheets` thickness are 1.3 mm and classified into two groups-no heating and 350 ℃ heating. Microstructure and mechanical properties have been investigated, and deformation behavior of the AZ31 sheets during single pass rolling has been discussed. Then, the prepared no heating AZ31 sheets was rolled for continuous multiple passes during two different processes-large reduction rolling and small reduction rolling. Microstructure,macrotexture and mechanical properties have been investigated, and deformation behavior of the AZ31 sheets during two different processes has been discussed.Main conclusions are as following:(1)During large reduction rolling, twinning dynamic recrystallization(TDRX) is main deformation coordination mechanism. With enhancing reduction ratio during single pass rolling,TDRX grains significantly enhance and intersect, which can unequally divide the deformed coarse grain into some grains. These grains can continuously coordinate deformation and be refined by DRX.(2)With reduction ratio 50%~60% during single pass rolling, microstructure of the AZ31 sheets appear obvious shear band, which can significantly weaken strength of the sheets. If continuing enhancing reduction ratio, the number of new fine grains largely increases, as a result of weakening the shear band and making strength recovery.(3)The AZ31 sheets during large reduction rolling have finer grains, less basal texture and better ductility.(4)After first rolling pass(passes), DRX new fine grains appear gathering in special orientation grain of large reduction rolling sheets, and scattering among grains of small reduction rolling sheets. The scattered fine grains surrounded by larger grains could be orientation locked,and coordinating ability of the surrounded fine grains could be suppressed. In contrast, thegathered fine grains surrounded by equally fine grains could have better coordinating ability due to interaction.(5)After annealing treatment at 350 ℃ +1 h, strength of the 0.2 mm sheets during two different rolling processes decreases, and ductility increases. However, the sheets produced by this rolling method are insensitive to this anneal condition.