| In this paper,the experimental study on the thermal bulging of AZ31 magnesium alloy sheet is carried out,including the thermal bulging test of magnetic pulse impact viscous medium and the thermal bulging test of quasi-static viscous medium.The effects of different discharge energies and different temperatures on the bulging of magnetic pulse impact viscous medium were systematically analyzed.The influence of the number of bulging times on the deformation law was also investigated.The comparative analysis of magnetic pulse and quasi-static forming process was revealed.The bulging law of viscous medium of AZ31 magnesium alloy sheet.The effects of different discharge energies and different temperatures on the forming properties of AZ31 magnesium alloy sheet and the forming law under different impact times were studied by magnetic pulse bulging test.The results show that:(1)at 25°C the sheet forming limit height is 11.13 mm.25°C~200°C with increasing temperature,AZ31 magnesium alloy sheet plasticity continues to improve the temperature sensitivity,When the temperature is raised from 25°C to 100°C,the forming height of the sheet is obviously improved,and the height change rate is36.08%;When the temperature is raised from 100°C to 150°C,the plasticity is further improved,but the height change is not obvious,and the height change rate is 1.09% at this time;At 200°C,the magnesium alloy sheet has the best forming performance,the forming limit height is 20.83 mm,and the maximum main strain is 21.14%.(2)At25°C~100°C,the relative wall thickness reduction rate of the second bulging workpiece is 5.8%,7.3%,respectively;and the primary bulging shape is 6.8%,9.1%,respectively,compared to the primary bulging,twice The wall thickness of the bulging workpiece is more uniform,and the wall thickness variation rate of the same bulge is also smaller.At 200°C,the maximum forming height of a bulging workpiece is 15.45 mm,the maximum strain is 17.69%,and the maximum bulging height of the secondary bulging workpiece is 20.83 mm,and the maximum principal strain is21.14%,indicating that the increase of the impact number can significantly improve the sheet forming performance.Through the comparison of the magnetic pulse bulging test and the quasi-static bulging test,it is found that:(1)At 25°C,the plate forming limit height is 12.74 mm under quasi-static conditions,which is basically consistent with the magnetic pulseresults.At 200°C,the plate forming limit height under quasi-static conditions is 24.62 mm,the maximum principal strain is 45.96%,and the forming limit height difference is 3.79 mm.This may be due to the energy loss and impact rate between the driving piece and the punch in the magnetic pulse test.(2)Under the conditions of this test,the quasi-static working hardening is not much different from the magnetic pulse at25°C.The quasi-static and magnetic pulse processing hardening phenomenon is obvious at 100°C,and the magnetic pulse processing hardening phenomenon is not at200°C.Obvious,and quasi-static still has some work hardening phenomenon.The microscopic mechanism of the AZ31 bulging member was investigated by SEM and optical microscopy.At 25°C,the fracture morphology of the bulging part was mainly composed of a small amount of dissociated fractures in the “river pattern”,and the crystallites were slightly elongated with a small amount of twins;At 100°C,the grain of the primary bulging of the magnetic pulse begins to refine,the secondary bulging grain has obvious refinement,and the quasi-static also has grain refinement,but there is no obvious secondary bulging;At 200°C,the magnetic pulse and quasi-static exhibit distinct microscopic deformation mechanisms.Under the condition of magnetic pulse,a large number of twins appear,the grains are large and have a tendency to grow,and quasi-static has obvious grain refinement and dynamic recrystallization. |
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