AZ31B在腐蚀环境下的棘轮与低周疲劳性能研究

Ratcheting and Low-Cycle Fatigue Characteristics of AZ31B Under Corrosive Environment

开发了适用于镁合金圆棒试样的在线腐蚀疲劳系统，通过在空气和磷酸盐缓冲液(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3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、应力幅值、腐蚀环境以及最大压应力对AZ31B的低周疲劳寿命的复杂影响，采用FP参数模型对AZ31B进行了寿命预测．基于修正的FP参数模型，较好地预测了AZ31B在腐蚀环境下的低周疲劳寿命．

An on-line corrosion fatigue testing system for Mg alloy round bar specimens was developed. Throughperforming cyclic fatigue tests under the environments with and without phosphate buffer solution(PBS), the ratchetingand low-cycle fatigue properties of an as-extruded AZ31B alloy were investigated. Results show that in the threestages of ratcheting strain evolution, the ratcheting strain rates of specimens tested in air and corrosive environmentwere similar at the transient and steady stages. Corrosion rate and ratcheting strain of Mg alloy increased with thestress amplitude and mean stress. The occurrence of twining and de-twining further increased the sensitivity to thecorrosive environment. The fatigue life of the Mg alloy in corrosive environment was significantly shorter than that inair and its reduction ratio of fatigue life to that in air could vary from 50% to 90%. To reflect the effects of mean stress,stress amplitude, corrosion environment and maximum compressive stress on the fatigue behavior, a FP parametermodel was employed for predicting the fatigue life of AZ31B. Based on the modified FP parameter model, the predictedlow-cycle fatigue lives of AZ31B under corrosive environment can be well fitted with the experimental results.