镁合金棘轮行为微观机制研究

项目名称： 镁合金棘轮行为微观机制研究

项目编号： No.50801038

项目类型： 青年科学基金项目

立项/批准年度： 2009

项目学科： 金属学与金属工艺

项目作者： 张新平

作者单位： 南京理工大学

项目金额： 20万元

中文摘要： 通过控制退火工艺、挤压比和、轧制压下量和试样取向获得了不同微观组织和静态力学性能的镁合金试样。AZ31镁合金经过挤压后，晶粒细化明显，提高了静态力学性能。在8到32的挤压比范围内，挤压比为16时可以得到最细的晶粒和最佳的力学性能。轧制后AZ31镁合金出现孪晶，压下率越大，孪晶越多，晶粒尺寸越小，强度增高，延伸率降低，各向异性明显。取样角度为 90 时的强度较高，0 时延伸率较差。 随循环次数增加，AZ31与AZ91D两种镁合金首先循环软化，然后循环硬化，并最终达到循环稳定。随平均应力和峰值应力的增加，棘轮应变增加。力学性能高、组织均匀的材料的抗棘轮行为能力高。加载历史对棘轮行为存在影响。 挤压和轧制不影响AZ31镁合金的循环软化/硬化特性，最后的棘轮应变随平均应力和峰值应力的变化趋势，但影响最后的棘轮应变随应力幅值的变化趋势。随挤压比和轧制压下量的增加，AZ31镁合金的棘轮应变减小，且加载历史对棘轮行为的影响也降低。 建立了基于Voronoi图的多晶体模型，数值模拟其棘轮行为规律及微观组织变化。棘轮行为数值模拟的结果与实际试验吻合较好。多晶体的应力应变分布与外应力的大小及内部晶粒取向有

中文关键词： 退火;棘轮行为;镁合金;塑性变形;微观组织

英文摘要： Mg alloy samples with different microstructures and static mechanical properties were obtained using extrusion, rolling, annealing treatment and orientation. The mean grain size decreased and the yield strength increased significantly with the extrusion ratio until the extrusion ratio reached 16, and thereafter the extrusion ratio had little effects. After rolling, twins were appeared in AZ31 magnesium alloy sheets. There were more twins and the grain size was smaller with the increase of reduction rate. Besides, the strength increased, and the elongation decreased. The anisotropy was obvious. The strength was highest when the angle was 90 while the elongation was smallest when the angle was 0 . Both of AZ31 and AZ91D Mg alloys presented the following characteristic behavior with increasing number of loading cycles: first an apparent cyclic softening was observed, then a cyclic hardening occurred, and finally a stable state was reached. The ratcheting strain of AZ31 magnesium alloy and AZ91D magnesium alloy increased with mean stress and stress amplitude. The load history influenced the ratcheting behaviors of these Mg alloys. Higher yield strength and more homogenous will decrease the ratcheting strain. The extrusion ratio and the rolling reduction did not influence the cyclic softening/hardening behavior or the final ratcheting strain variation trend of the extruded AZ31B Mg alloy with the mean stress and the peak stress. However, the extrusion ratio influenced the final ratcheting strain variation trend of the extruded AZ31B Mg alloy with the stress amplitude. Increasing the extrusion ratio and the rolling reduction also reduced the ratcheting strain and the effects of the load history on the ratcheting behavior of the extruded AZ31B Mg alloy. A polycrystalline model based on Voronoi figure was built and the variation of ratcheting behaviors and microstructures was simulated. The simulation results agreed with the experimental ones. The stress and strain distribution of the polycrystalline model was determined by the stress outside and the grain orientation.

英文关键词： Annealin; Ratchetting behaviour; Magnesium alloy; Plastic deformation; Microstructure