镁合金AZ31B的棘轮-低周疲劳-腐蚀交互作用研究-化学工程(化工过程机械)专业毕业论文.docx

万方数据 万方数据 中文摘要 镁合金由于具有其密度低、比强度高、机械加工性能好，以及生物相容性 等优点，使其在轻量化设计和生物移植材料中的应用越来越广泛。AZ31B 作为 重要的承载结构部件或生物移植材料，对其棘轮应变性能和腐蚀疲劳性能的研 究具有重要现实意义。 本文开发了适用于镁合金圆棒试样的在线腐蚀疲劳系统，通过在空气和模 拟体液（PBS）中分别进行循环疲劳试验，研究了腐蚀环境对 AZ31B 棘轮和低周 疲劳性能的影响。结果表明：在棘轮应变演化的三个阶段中，腐蚀环境下试样 在瞬态阶段和稳态阶段的棘轮应变率与空气中的相似；镁合金的腐蚀速率和棘 轮应变随应力幅值和平均应力的增大而增大，孪晶、退孪晶的出现使得试样对 腐蚀环境的敏感性进一步增加；在腐蚀环境中，镁合金的疲劳寿命大幅缩减， 与空气中的试验相比，寿命缩减率达到 50%-90%；为了能够反映平均应力和应 力幅值等加载条件以及腐蚀环境对 AZ31B 低周疲劳寿命的复杂影响，本文采用 Ellyin 能量法模型和 FP 模型对 AZ31B 进行了寿命预测，并对这两个模型进行评 估、修正，最终修正 Ellyin 能量法模型较好地预测了 AZ31B 在腐蚀环境下的低 周疲劳寿命。 关键词：低周疲劳；棘轮；镁合金；腐蚀疲劳；寿命预测 ABSTRACT Wrought magnesium alloys are very attractive for lightweight design and biological materials justified by their low density, high strength-to-weight ratio, high specific stiffness, good machinability and recyclability. It have great significance to evaluate the low cycle fatigue (LCF) properties of magnesium alloys, and give an insight into the studies on the corrosion fatigue properties of magnesium alloys. A miniaturized corrosion fatigue testing system for round bar specimens was developed. Through performing cyclic fatigue tests under the environment with and without corrosive medium, the ratcheting and low cycle fatigue properties of an as-extruded AZ31B alloy were investigated. In the three stages of ratcheting strain evolution, the ratcheting strain rate of specimen testing in air and corrosion environment was similar at the transient and steady stages. Corrosion rate and ratcheting strain increased with the stress amplitude and mean stress. The occurrence of twining and de-twining further increased the sensitivity to the corrosion environment. The fatigue life of the alloy in PBS solution was significantly shorter than that in air and its reduction ratio of fatigue life to that in air could vary from 50% to 90%. To reflect the effects of mean stress, corrosion and maximum compressive stress to the fatigue behavior, FP parameter fatigue life model and Ellyin’s energy model were emplo