Continuous Casting Of The Organizational Structure And Annealing Behavior Of The Az31b Magnesium Alloy Slab

AZ31 Mg alloy plate blank has been fabricated by twin-roll casting technology,and then the microstructure and anneal behavior of the plate blank have been analyzed by optical microscope,scanning electron microscope,transmission electron microscope,energy spectrum analysis, X-ray diffraction and Vickers hardness testing.Finally,the conclusions were obtained as follows:(1) The phases in twin-roll casting AZ31 Mg alloy plate blank includedα-Mg dendritic,along with divorced eutectic that made up of enrichedα-Mg and coarse Mg₁₇(Al,Zn)₁₂ phase distributing in interdendritic,as well as the fine star-shaped Al₈Mn₅ phase dispersing in the dendritic.(2) The plate blank has undergone some plastic deformation during twin-roll casting process,but the deformation is inhomogeneous. Macroscopically,the deformation distributed more near the plate surface,because of the different stress conditions between the surface and the centre,which are lead by the friction of cast rolls. Microscopically,dislocations stacked near the grain boundaries and lead the stress concentration,then the non-basal slip has been activated at these areas.This lead the formation of the dislocation nets and make the dynamic recovery and dynamic recrystallization take place and lead the plastic deformation concentrate near the grain boundries.(3) The plate blank showed anisotropies of microstruture and property remarkably,which indicate that the texture has formed as a result of the effect of directional solidification and hot rolling of casting rolls; the texture near the surface and at the centre are different.Near the surface the texture is(0001)[11(?)0]+(0001)[21(?)0],and at the centre that could be expressed as(10(?)4)[(?)021]+(11(?)4)[10(?)0]approximately.(4) Recrystallization take place rapidly during uniform anneal at 430℃. The inhomogeneous deformation of original structure lead the recrystallization start at the original grain boundary,and then extended to the core.Recrystallization completed after anneal for 2 hours.No new texture has been formed during annealing.As recrystallization going on,original structure was consumed and the original textures were weaken.After uniform anneal,the dentritic segregation and the work-hardening have been eliminated,the basal texture has been weaken and the homogeneous orthoscopic recrystallized structure was gained,all of these would do good to subsequent deformation.