Research On The Microstructural And Textural Control Of Magnesium Alloy AZ31Sheet During Rolling Deformation

Rolled magnesium alloy is the "21th century green structural metal" whichhas been widely used in many fields nowadays. The microstructure and textureof the rolled sheet are the leading control factors of its processability andusability. It is a hot topic recently the microstructural and textural optimizationsof the rolled magnesium alloy for extending its application. Therefore, the coreproblem to optimize the producing process and improve the quality of product isto predict and control the microstructural and textural evolutions of magnesiumalloy sheet during rolling deformation.The present work studied the rule and mechanism of the microstructuraland textural evolutions for magnesium alloy sheets during rolling deformation.The factors causing the microstructural and textural differences were analyzed,and the rule and affecting factor of the critical deformation mechanism havebeen discussed throughly. Then this paper attempt to develop a model for themicrostructural and textural prediction based on the theoretical study, so as tooptimize the rolling process for the wrought magnesium and producemagnesium alloy sheet with better mechanical performance.Some results are obtained as follows:Scanning electron microscope (SEM), electron back-scatter diffraction(EBSD), and X-ray diffraction (XRD) have been applied on the magnesiumalloy AZ31for the investigation of microstructural and textural evolutionsduring different rolling processes. The influences on the microstructure andtexture of the rolled sheet have been discussed taking into account of the initialtexture, rolling temperature and rolling method. The results show that twinningis the root causes of the microstructural and textural differences of the rolledsheet.The twins in a magnesium alloy sheet rolled to9%at150oC have beeninvestigated statistically. A "strain accommodation rule" has been proposed forexplaining the twin variant selection phenomena physically. A simplifiedSchmid factor "SFrolling" was proposed for rolling deformation, and has been physically interpreted in the view of external strain accommodation. Therefore,the "abnormal twins" with negative SFrollingvalues could be explainedreasonably. A new method "strain map" was applied to show the strainaccommodation of the twins. It has been discussed thoroughly the iflences of theexternal and self strain on the double twin variant selection through the newmethod. The effects of the rolling strain, rolling temperature and deformationmode on the "strain accommodation rule" have been studied carfully. Theinfluencing mechanism of these affecting factors has been discussed as well asthe application scope of the rule.Furthermore, on the foundation of the "strain accommodation rule", asimple crystal plasticity model has been developed for predicting the influencesof the double twins on the microstructural and textural evolutions of magnesiumalloy sheet during rolling deformation. The predictions coincided well with theexperimental results. The result indicated the reliability of the twin variantselection rule. A thin magnesium alloy sheet with less ductile anisotropy and nostrength loss has been produced through an optimized warm rolling process. Thequality of the product has been improved therefore.