| Magnesium alloys are widely used in the fields of electronic communication,automobile manufacturing,aerospace and so on,and they are regarded as "the most promising green engineering materials in twenty-first Century".But magnesium alloys have poor formability and toughness under room temperature condition due to the hexagonal close-packed structure,which is the key problem to limit its processing technology.In this paper,the test material was AZ63 magnesium alloy,and magnesium alloy sheet was prepared by different ARB process(Accumulative Roll Bonding,ARB),to deal with the practical problem of the poor formability of magnesium alloy at room temperature,and the limitation of application market.Then a new research idea was pointed out,that is by adjusting and controlling the microstructure of magnesium alloy sheet using accumulative roll bonding process,thus the comprehensive properties of the material are improved.That is to say,the microstructure and properties of magnesium alloy can be refined by accumulative roll bonding,and the theory of plastic deformation of magnesium alloy is improved,to provide theoretical basis and guidance for practical application.The accumulative roll bonding tests of AZ63 magnesium alloy were performed at deformation temperature range of 250-400? and 5 passes ARB deformation were performed at each temperature.The effects of accumulative roll bonding on the interfacial bonding behavior,microstructure and properties of magnesium alloy sheet were investigated by means of microstructure observation and mechanical property test,then the interfacial bonding mechanism,ARB plastic deformation mechanism and grain refinement mechanism were thoroughly analyzed.The results show that the grain structure of magnesium alloy sheet can be effectively refined,and the strength and plasticity of the material can be improved by accumulative roll bonding process,and with the increase of the passage,the homogeneity of the structure was improved obviously.After ARB3 passes,the strength can be increased from the original 232 MPa to 282 MPa,the rate of elongation was greatly increased to 26.3% by ARB1 pass.The deformation temperature and first pass deformation are the key factors restricting the interface quality.To Increase the heating temperature and prolonging the holding time,can not only effectively improve the plastic deformation of magnesium alloy,but also help the interface bonding;The bonding quality of the previous interface has been improved gradually in the subsequent rolling,and the interfacial bonding mechanism of the accumulative roll bonding is the mechanism of recrystallization bonding.Twinning plays an important role in the Accumulative Rolling Process of magnesium alloy,which is beneficial to the slip of the base surface,and at the same time induces a large number of recrystallization,which results in the formation of shear bands.The orientation of shear band is favorable for the start-up of the base slip,and can accommodate more external deformation by extending and broadening,so as to improve the plastic deformation ability of the material.With the accumulation of deformation,the degree of recrystallization increases,and the shear band disappears.Based on the plastic deformation mechanism of magnesium alloy and the nucleation mechanism of recrystallization,the twinning induced recrystallization nucleation model was established: it is easy to produce stress concentration at the intersection of twins,which provides the deformation energy storage for the recrystallization,and the twin boundary becomes the effective nucleation point.The stronger the interaction of twins is,the more the nucleation sites are,the more favorable the grain refinement effect is.For the ARB deformation of AZ63 magnesium alloy,the grain refinement is due to the large cumulative deformation and the surface shear deformation. |
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