【作者】 闫富华；

【导师】 张喜燕；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2011， 硕士

【摘要】 动态塑性变形可以实现材料的高速变形,通过简单调节工艺参数就可方便控制形变试样的微观组织特征,从而达到控制相关性能的目的,目前,已经利用动态塑性变形技术制备出了多种面心立方金属合金纳米/超细晶结构材料。镁及镁合金在室温的变形能力较差,本文研究镁及其合金在动态塑性变形时的变形机理,和动态塑性变形后的力学性能,试图通过动态塑性变形制备细晶镁及镁合金,从而提高材料的力学性能。采用对比试验研究动态塑性变形前后纯镁及AZ31镁合金的力学性能变化,通过测试了拉伸性能和硬度,并借助金相显微镜、X射线衍射仪、扫描电子显微镜和背散射电子衍射技术研究材料力学性能变化的主要微观机制。纯镁动态塑性变形前的状态为热压退火态,室温动态塑性变形后不经过退火,为研究动态塑性变后纯镁力学性能的变化,本文引入了室温下的准静态压缩试验,补充研究动态塑性变形对纯镁力学性能的影响。纯镁的拉伸试验中采用了5种应变速率,热压退火态按拉伸轴与试样C轴之间的夹角,将试样分为0°、30°、60°和90°等4种角度的拉伸试样,动态塑性变形试验中,按加载力方向与试样C轴之间的夹角,也分为0°、30°、60°和90°试样,动态塑性变形后纯镁的拉伸方向均与试样在动态塑性变形时外力的加载方向垂直,室温准静态压缩试验与动态塑性变形相似,拉伸试验也一致。AZ31镁合金动态塑性变形前的状态是热轧退火态,试样内没有孪晶,有粗大的晶粒存在,并有较强的织构,所有拉伸试验均在0.01%/s、0.1%/s和1%/s等3种应变速率下进行,热轧退火态试样的拉伸实验与热压退火态纯镁相似,也按拉伸轴与试样C轴之间的夹角,将试样分为0°、30°、60°和90°等4种角度的拉伸试样,动态塑性变形时外力的加载方向与试样的C轴垂直,不同动态塑性变形应变后的AZ31镁合金拉伸试样按拉伸轴与动态塑性变形时外力的加载方向之间的夹角,分为0°、30°、60°和90°等4种角度。研究表明,纯镁发生8%的动态塑性变形后,各角度试样都具有基面织构特征,织构的C轴与动态塑性变形时外力的加载方向平行,90°纯镁试样形成了孪晶/基体的片层组织,片层厚度约5μm,晶粒尺寸略有减小,且分布较均匀,动态塑性变形后纯镁具有最高的抗拉强度和硬度值,延伸率降低,但90°纯镁试样动态塑性变形后壁室温压缩后的延伸率较大。AZ31镁合金发生不同应变量的动态塑性变形后,屈服强度和抗拉强度都升高,当动态塑性变形5%后90°试样的强度和延伸率都被提高,其它动态塑性变形应变量下的延伸率有不同程度的减小,同时,动态塑性变形变形量较小时,试样的断裂脆性得到改善。动态塑性变形后纯镁和AZ31镁合金强度的增加主要原因有3个,即动态塑性变形后晶粒内有较高密度的位错、高密度的孪晶界和粗大晶粒的细化,动态塑性变形对纯镁和AZ31镁合金延伸率的影响主要是通过高密度的位错滑移,和位错与孪晶之间的交互作用调节材料的塑性,另外,动态塑性变形使粗大的晶粒细化,有很好的细晶强化作用,也能够提高材料的塑性。更多还原

【Abstract】 Dynamic plastic deformation can make a material deform with a huge strain rate,some mechanical properties could be achieved by sample adjustment of process witch can control microstructure characteristics of materials,at present,a variety of nano and super fine-grain face centered cubic metals and alloys has been developed using dynamic plastic deformation. The deformation ability of magnesium and its alloys under room temperature is poor,the deformation mechanism of dynamic plastic deformation and its influence on mechanical properties of pure magnesium and AZ31magnesium are discussed,dynamic plastic deformation method is used to get fine magnesium and its alloy so as to prove its mechanical properties.The influence of dynamic plastic deformation on magnesium and AZ31 magnesium alloy is researched by contrast experiments,mainly tension properties and hardness tests,researching in the micro mechanism of tension deformation by means of a serial analysis with metallographic examination microscope,X-ray diffraction,scanning electron microscope (SEM) and backscatter electron diffraction (EBSD) technology. As initial samples,pure magnesium has been pressed under 450℃and then annealed,dynamic plastic deformation is achieved under room temperature without anneal process,strain is 8%,quasi-static deformation is added for study in pure magnesium,defines four kinds of tension samples according to the angle between tension and C axis,respectively 0°,30°,60°and 90°samples,there are five tension rates. There are four samples according the angle between C axis and loading direction(LD) during dynamic plastic deformation experiment,however,the tensile direction are both perpendicular to the LD after dynamic plastic deformation,other tension conditions are the same as the initial pure magnesium. AZ31 magnesium alloy is attended by means of hot rolled followed with annealing,there are no twins but some large grains,and has a strong texture,the tension rate includes 0.01%/s,0.1%/s and 1%/s,there are four kinds of tension samples like initial pure magnesium. AZ31magnesium alloy deformed with different strain in dynamic plastic deformation experiments,and then developed new C axis,so the tension samples are defined according angles between tensile direction and new C axis,including 0°,30°,60°and 90°samples.Research shows that the texture of pure magnesium are changed after 8% dynamic plastic deformation except 0°sample,and new C axis parallel to the loading direction, many twin/matrix lamellar abrupt appear in 90°sample,the mean thickness is about 5μm,and large grains disappear,grains are in a uniformly distribution,although pure magnesium has a largest strength after dynamic plastic deformation,the elongation are decreased,however,the elongation of 90°samples dynamic plastic deformed are better than pressed under room temperature. The yield strength and tensile strength of AZ31magnesium alloy are improved after dynamic plastic deformation,in witch the texture are changed. Both strength and elongation are increased after dynamic plastic deformed 5%,but are decreased in other strain samples. Brittleness of AZ31 magnesium alloy is improved if the strain is small in dynamic plastic deformation.There are three main reasons for increase in strength for dynamic plastic deformed AZ31 magnesium alloy,the high dense dislocations and twin boundaries,as well as finer grains,the influence of dynamic plastic deformation on the elongations of pure magnesium and AZ31 magnesium alloy is based on high dense dislocations and twins,and their interactions,besides these tow actions,dynamic plastic deformation can refine grains and then improve the plasticity of materials.更多还原