| Magnesium alloys have been widely favoured in various fields due to its excellent properties.In recent years,our country have paid more attention to research and develop the magnesium alloys.This topic choose the rolling AZ31 magnesium alloy thin sheets as the research material.This paper studied the mechanism of twins appearance and change,studied the the influence of twinning,detwinning and recrystallization on microstructure and formability of AZ31 magnesium alloy thin sheets on the basis of presetting twins by pre-compressing after a certain number of annealing process by combining the observation of microstructure and experiments of mechanical properties.We came to the following conclusion by the study of this paper:(1)In order to study the initial twins on the microstructure and formability of magnesium alloy thin sheets(1 mm),pre-compression was conducted along transverse direction(TD)and rolling direction(RD)with 1.59%,3.32% and5.38% strain levels,respectively.Then annealed at 200 ? for 6 h to removestress and keep twin lamellar structure.The results found that the yield strength(YS),the ultimate tensile strength(UTS)and fracture elongation(FE)improved with pre-compressive levels increasing.At the same time when TD pre-compression then reverse uniaxial tension and RD pre-compression then reverse uniaxial tension were conducted,the true stress-strain curves showed the yield platform,which can attribute to the happening of the detwinning.With the increasing of pre-compressive levels,the n-value of materials increased and the r-value of materials decreased,and the IE-value of TD pre-compression specimens increased from 2.83 mm of the original one to 5.36 mm of the largest pre-compression degree,increased by 89.40% compared with the original one.However,the IE-value of RD pre-compression specimens increased from 2.83 mm of the original one to 6.78 mm of the largest pre-compression degree,increased by 139.58% compared with the original one.The formability of pre-compression specimens increased,also the formability of RD pre-compression specimens was stronger than the TD pre-compression specimens.(2)TD pre-compression 5.20% was conducted.And then annealed at different temperature of 200?,300?,400? and 500? for 2 h.We found that the grain size increased and then decreased.When annealed at 400 ?,the grain size increased from 9.6?m of the original one to the largest 32.9?m.When annealed at 400 ? from 10 s to 120 s,the volume fraction of twins decreased gradually,and twins disappeared completely at 120 s,which explained thatrecrystallization rate induced by twins happens quickly.The yield strength(YS)and the ultimate tensile strength(UTS)at three directions(RD,45°and TD)decreased,and fracture elongation(FE)decreased,but the n-value of materials increased and the r-value of materials decreased with the increasing of annealing tempareture.The formability of thin sheets increased gradually with the increase of grain size.The IE-value increased from 2.83 mm of the original one to 5.78 mm of anneal at 400?,increased by 104% compared with the original one.(3)TD pre-compression was conducted with 1.59%,3.32% 5.38% and7.76% strain levels respectively,and then high temperature annealed at 450 ?for 2 h.We found that the grain size increased gradually from 9.6 ?m of the original sheet to 14.2,31.3,32.1 and 35.3?m with pre-compressive levels increasing.Also yield strength(YS)decreased,ultimate tensile strength(UTS)and fracture elongation(FE)increased gradually.The r-value of materials decreased and the n-value of materials increased gradually.The IE-value of TD pre-compression specimens increased from 2.83 mm of the original one to 3.6,5.09,5.43 and 5.74 mm,the formability increased by 103% compared with the original one.(4)TD pre-compression 1.69%,3.32% and 5.38% and following RD pre-compression 3.3% was conducted,then annealed at 450 ? for 2 h.Pre-deformation made(0002)base rotate nearly 90° and produced a large number of twins.Subsequent annealing had no effect on(0002)basal texture,but eliminated the twins and appeared some tiny recrystallization grain,thus theplasticity of magnesium alloy improved.With TD pre-compressive levels increasing,grain size increased gradually,the grain size increased from 9.6?mmm of the original one to 25.6?m mm of the largest pre-compression degree.The yield strength(YS),the ultimate tensile strength(UTS)decreased gradually,and fracture elongation(FE)improved with TD pre-compressive levels increasing.The n-value of materials increased and the r-value of materials decreased,and the IE-value of pre-compression specimens increased from 2.83 mm of the original one to 5.61 mm,5.72 mm and 6.01 mm,the formability of pre-compression specimens increased obviously,increased by 112.3%.(5)RD pre-compression 3.3% and following TD pre-compression 1.69%,3.32% and 5.38% was conducted,then annealed at 450 ? for 2 h.With TD pre-compressive levels increasing,grain size decreased gradually.The grain size of the original one was 9.6?m,and the grain size of different pre-compressive levels were 27.1,18.9 and 17.1?m.Which may be related to that RD pre-compression promote critical deformation of recrystallization reduce,recrystallization nucleation rate was greater than the growth rate when pre-compression levels went beyond the ritical deformation.The IE-value of pre-compression specimens were 4.88 mm,5.37 mm and 5.48 mm,respectively,which showed that the change of the grain orientation was greater than the influence of grain growth and texture weakening on formability. |
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