Study On Rolling Process Of Fine Grain ZK60 Magnesium Alloy Sheets

Magnesium alloy sheets are widely used in the fields of electronics,transportation and aerospace.During the rolling deformation process,there is an effective method to improve the strength and plasticity of the magnesium alloy sheet by strengthening the dynamic recrystallization behavior to achieve the grain refinement and controlling the nanophase precipitate.In this study,ZK60 alloy sheets are produced by a single pass rolling process with a large reduction of 80%.The microstructure evolution and mechanical properties rolled at the temperature ranging from 275℃-350℃ and strain rate ranging from 5 s-1～25 s-1 are studied.The effects of strain rate on dynamic precipitation behavior and interaction between precipitation and deformation mechanism are investigated.The results are mainly concluded as follows:(1)The degree of recrystallization of ZK60 alloy is promoted by increasing the strain rate and increasing the rolling temperature.The highest volume fraction(96.7%)of dynamic recrystallization(DRX)are obtained at the temperature of 350℃ and the strain rate of 25 s-1.At the temperature lower than 300℃,increasing the strain rate,the DRX grain size decreases firstly and then increases,the minimum grain size(1.2μm)obtained at the temperature of 300℃ and the strain rate of 10 s-1.At the temperature higher than 300℃,the DRX grain size increases firstly then decreases,and then increases with the increase of strain rate.(2)When the sheet is rolled at low strain rate(5 s-1),the degree of recrystallization is quite low,and a lot of dislocations exist in the un-DRX region,which leads to the high strength but poor plasticity.Increasing the stain rate to 10 s-1～-20 s-1,the sheets have a balance of mechanical properties with the fine and uniform recrystallized structure.When the sheet is rolled at the strain rate of 25 s-1,the strength decreases due to the coarsen of DRX grain size.The optimal mechanical properties are obtained at the temperature of 300℃ and the strain rate of 10 s-1,the tensile strength,yield strength and elongation are 358MPa,291MPa and 21.5%respectively.(3)When the sheets are rolled at the temperature of 300℃,the basal texture of ZK60 alloy is significantly weakened by increasing the rolling strain rate,which is beneficial for the activation of basal slip system during tensile deformation at room temperature,thereby improving the plasticity.(4)During the rolling process,the second phase is mainly precipitated on the dislocations.The strain rate affects significantly the size and distribution of the precipitates.The precipitates with the larger size and the larger density are obtained at the strain of 5 s-1 with increasing strain rate,the size and the density of precipitate decrease gradually.(5)The dynamic precipitates suppresse the DRX process by pinning the dislocations and the grain boundaries.The effects of precipitates on the DRX are various at the different rolling strain rates.The precipitates exhibit an inhibiting effect on DRX nucleation at the strain rate of 5 s-1;and mainly retard the DRX growth at the strain rate of 10 s-1;while a little effect on the DRX nucleation and growth is achieved at the strain rate of 25 s-1.