Tailoring The Texture And Mechanical Properties Of Mg-2Zn-1.2Ca Alloy Sheets By Different Cold Rolling Paths

As the main products of wrought magnesium,magnesium alloy sheets are inclined to produce a strong basal texture during rolling processes,which is harmful to the subsequent plasticity deformation.Therefore,it is crucial to develop new sheet rolling process and heat treatment process to improve the plasticity deformation capacity of magnesium alloys for the expansion of their application.It was reported that a double peak non-basal texture largely tilting from ND could formed in magnesium alloy sheets after rolling within the addition of rare earth element.The texture intensity weakens at the same time.But the high cost of rare earth element limits their application expansion.Cheap calcium presents similar effects to rare earth elements.Combined with the research results above,unidirectional and multidirectional cold rolling processes are conducted using as-hot-rolled Mg-2Zn-1.2Ca(wt.%)magnesium alloy slab.Effects of different cold rolling paths and heat treatment processes on the microstructure,crystal orientation and mechanical properties of Mg-2Zn-1.2Ca(wt.%)magnesium alloy sheets were investigated.The main contents and results of this thesis show that:(1)The cold rolling paths affect the distribution characteristic of Mg-2Zn-1.2Ca alloy sheets.Unidirectional rolling sheets tend to develop a double peak texture,while the multidirectional rolling sheets present a circle like deformation texture.So the changing of rolling paths can effectively control the distribution of deformation texture.(2)Different rolling paths have certain effects on the grain size and its distribution of sheets after annealing at 360?C.Compared with unidirectional rolling sheets,the grain size of multidirectional rolling sheets is refined to a certain extent,and the grain size distribution is more uniform.However,the grain size differences are not obvious at a higher temperature of 400?C.(3)The recrystallization textures are affected by cold rolling paths.Unidirectional rolling sheets develop double peak non-basal textures perpendicular to the rolling paths after annealing,while circle like textures are formed in multidirectional rolling sheets.The c-axis of recrystallized grains deviate from ND more widely when extending the annealing time,and higher annealing temperature will increase the texture dispersion.(4)Most recrystallization grains of unidirectional rolling sheets orientate perpendicular to the rolling paths at the early stage of nucleation.A few random orientated grains will be merged by the grains orientating perpendicular to the rolling paths in the process of grain growth.In addition,the recrystallized grains of non-basal orientation have the advantage of growing,which weaken the final basal texture.It can be concluded that the formation of recrystallization textures are both controlled by the directional nucleation mechanism and the selective growth behavior of recrystallized grains.(5)The annealed unidirectional rolling sheets possess remarkable anisotropy of yield strength.The yield strength anisotropy of annealed multidirectional rolling sheets significantly decrease,and the comprehensive performance is higher than that of annealed unidirectional rolling sheets.