Effects Of Texture On Formability Of Rolled ZK60 Magnesium Alloy Sheets At Room Temperature

Based on its small specific gravity and high specific strength,magnesium alloy sheets are widely used in electronic products,automobiles,aerospace and defense.However,subject to the crystal structure of hexagonal close packed crystal lattice,the plate is easily formed into a strong basal texture during the rolling process,resulting in a high yield ratio(?0.8)and a low work hardening rate of the plate(especially fine crystal plate).It is prone to performance anisotropy,which is extremely unfavorable for deep processing of sheets(such as bending,torsion,press forming,etc.),which greatly limits the development of magnesium alloys.In the current researches,there are few studies on the influence of texture on the forming properties of magnesium alloy sheets,and the influence mechanism is not clear.To this end,this subject uses ZK60 magnesium alloy sheet as the research object,using different hot rolling methods and cumulative cold rolling process to prepare fine-grained magnesium alloy sheets with different texture states,and then based on “uniaxial stretching,plane strain and double-stretching”,the Bulging experiment was carried out.The tensile deformation experiment was carried out to study the room temperature forming behavior of magnesium alloy sheets under the influence of texture,and the influence of texture state on sheet forming properties was analyzed.Three kinds of hot rolling processes,extrusion-rolling,extrusion-asynchronous rolling and multi-pass rolling,were combined with the cumulative cold rolling annealing process to prepare fine-grained ZK60 magnesium with different texture states.This paper studied the evolution of the microstructure and mechanical properties of the sheet during the rolling process.The results show that all the hot rolling processes can obtain fine-grained magnesium alloy sheets with grain size less than 8?m.However,the multi-pass cooling rolling produces a strong base texture while refining the grains,and the extrusion-rolling and the extrusion-asynchronous rolling can all weaken the basal texture of the sheets.Three kinds of plates with different texture states were selected for uniaxial stretching,plane strain and double-stretching forming experiments at room temperature.The results show that the forming limit of the weak texture direction of the sheet is higher than that of the strong texture direction.For single-drawing specimens,when the lengthwise direction texture of the specimen is weaker and the width direction is stronger,the deformation in the longitudinal direction is mainly dominated by the basal slip,and the deformation in the width direction is {10-12} tensile twinning leading.When the texture in the lengthwise direction is weaker than the width direction,the deformation in the longitudinal direction is dominated by non-basal slip,and the deformation in the width direction is dominated by {10-12} tensile twinning.For the plane strain test piece and the bidirectional isometric test piece,the deformation in the first principal strain direction is dominated by the basal slip,and the deformation in the second principal strain direction is dominated by the non-basal slip.The strain distribution before the rupture of the three-plate tensile specimens was compared and analyzed.It was found that the first principal strain direction of the sheet was consistent with the weak texture direction of the sheet under the same stress conditions.According to the strain distribution and deformation mechanism during the bulging process of the sheet,the longitudinal direction of the single tensile specimen can be consistent with the weak texture direction of the sheet to obtain a higher forming limit;the longitudinal direction of the plane strain specimen can be consistent with the weak texture direction of the sheet.The high forming limit can be consistent with the strong texture direction of the sheet to obtain a larger second main strain;the forming limit of the bidirectional isometric specimen depends on the forming property of the sheet in the strong texture direction.