基于位错行为的稀土镁合金动态应变时效机理研究

Rare earth (RE) containing magnesium alloys have a good potential to be applied in the 3C, transportation and aerospace industries due to the advantages of high strength, good heat resistance, etc. However, under certain deformation temperatures and strain rates, dynamic strain aging (DSA) occurs in RE containing Mg alloys. The occurrence of DSA is usually very detrimental to the ductility and leads to an early failure of the structural parts. In this project, the mechanism of DSA in RE containing Mg alloys will be studied based on the dislocation behavior. The effect of deformation temperatures and strain rates on the DSA behavior will be investigated. Evolution of dislocation density and velocity will be determined to elucidate the cooperative influence of RE, Al and Zn. Types of dislocations activated under the DSA conditions and the distribution of RE atoms around the dislocations will be characterized to reveal the interactions between solute RE atoms and dislocations. The effect of composition, volume percentage, size and distribution of second phases on the mobility of dislocations will be studied as well. Based on the results of this project, the key influencing factors and controlling methods on the DSA behavior of RE containing Mg alloys will be discovered. Fundamental theories and novel ideas on alloy design and processing parameters will also be provided.

稀土镁合金具有强度较高、耐热性能较好等特性，在3C、交通运输和航空航天等领域有很大的应用前景。然而在特定温度和速率下变形时，稀土镁合金中会发生动态应变时效现象，使材料的塑性急剧降低，严重损害了其使用性。本课题拟从位错的角度出发研究稀土镁合金动态应变时效机理，考察温度和变形速率对稀土镁合金动态应变时效行为的影响；确定不同合金中位错密度及运动速率演变特点，阐明稀土元素与Al、Zn对镁合金中位错运动的共同作用；考察稀土镁合金在动态应变时效条件下开动的位错类型，探究稀土原子在不同类型位错周围的分布特点，揭示不同位错与固溶稀土原子之间的相互作用规律；探明稀土镁合金中第二相的成分、含量、尺寸及分布对位错运动行为的影响。基于本课题的研究成果，发掘稀土镁合金动态应变时效行为的关键影响因素和控制手段，为优化稀土镁合金的成分设计和生产加工工艺提供理论基础和新思路。

含稀土镁合金在一定条件下变形会产生锯齿状应力-应变曲线，同时塑性急剧降低，影响变形过程的稳定性，这是由于发生了动态应变时效现象。本项目研究稀土镁合金的动态应变时效行为。分析不同镁-稀土二元合金的高温变形行为，明确了变形条件以及稀土元素的种类和含量对镁合金动态应变时效行为的影响。通过高温DIC拉伸实验，揭示了镁合金中PLC带形成和扩展的机制及规律，阐明了动态应变时效在稀土镁合金高温变形过程中引起失效及表面质量降低的本质。研究了添加稀土元素对镁合金中第二相的作用，明确了添加稀土元素和钙对镁合金高温变形过程中位错行为的影响，并进一步完成了微合金化AZ31镁合金的高温变形行为研究。本项目研究成果可以被应用于指导变形稀土镁合金生产工艺的制定，有益于优化提高变形稀土镁合金产品的生产效率，提升镁合金行业的产能及产品质量，促进行业发展，扩大经济效益。