AZ31B镁合金压-压循环载荷下变形行为及变形机制演化EI北大核心CSCD

为探讨AZ31B挤压态镁合金棒材沿径向取样的循环变形特征,开展了0.75%,1.0%,2.0%和4.0%应变幅下应变控制的非对称压-压循环变形实验。结果表明:在小应变幅(0.75%,1.0%)下,循环变形的滞回曲线表现出较好的对称性;在大应变幅(2.0%,4.0%)下,滞回曲线对称性差,且在滞回曲线上出现拐点;随着循环周次增加,塑性应变幅呈现下降趋势,材料均表现出循环硬化行为,在小应变幅下循环拉伸阶段对材料硬化率远大于压缩阶段的硬化率,而在大应变幅下这种区别并不明显。分析表明,沿径向取向的〈1120〉丝织构镁合金,小应变幅下位错滑移在整个寿命周期内作用更大;大应变幅下,随着塑性变形的增加,循环过程中变形机制发生演化,较低临界剪切应力(critical resolved shear stress,CRSS)的基面位错和拉伸孪生不能完全满足变形要求,较高CRSS滑移系启动及残余孪晶使得滞回曲线出现拐点;循环变形过程中不完全的孪生-去孪生过程使基体中存在大量残余孪晶,影响了循环变形过程的硬化率,同时降低了疲劳寿命。

Deformation behavior and deformation mechanism evolution of AZ31B magnesium alloy under compression-compression cyclic loading

In order to investigate the cyclic deformation behavior in radial direction of extruded AZ31B magnesium alloy, the asymmetric compression-compression cyclic deformation test under strain-controlled was carried out at the strain amplitudes of 0.75%, 1.0%, 2.0% and 4.0%. The results indicate that the hysteresis curves of cyclic deformation show good symmetry at the small strain amplitudes of 0.75% and 1.0%. At the large strain amplitudes of 2.0% and 4.0%, the hysteresis curve shows poor symmetry, and the inflection point appears on the hysteresis curve. With the increase of cycles, the plastic strain amplitude decreases, and all materials exhibit cyclic hardening behavior. The hardening rate during tensile process is much higher than that of compression process at small strain amplitude, however the difference is not obvious at large strain amplitude. The analysis reveals that the effect of dislocation slip is greater on the entire life of magnesium alloy with 〈11${rm{bar 2}}$0〉 silk texture along the radial orientation at the small strain amplitude. At the wide strain amplitude, the deformation mechanism evolves during the cyclic process with the increase of plastic deformation, the base plane dislocation and tensile twinning of lower critical resolved shear stress(CRSS) can not fully meet the deformation requirements, while the initiation of slip system and residual twinning of higher CRSS cause inflection point of hysteresis curves. The incomplete twinning-detwinning process results in a large number of residual twins in the deformed matrix, which affects the hardening rate during the cyclic deformation process, the fatigue life is reduced in the meantime.