AZ31镁合金微区电偶腐蚀的数值研究

Numerical study on the micro-galvanic corrosion of AZ31 magnesium alloy

结合水平集函数方法及移动网格技术,利用有限元法模拟分析了离散型β相分布和连续型β相分布的AZ31镁合金在NaCl溶液中的腐蚀行为,通过解Nernst-Planck方程得到腐蚀过程中AZ31镁合金/NaCl界面的电势、氯离子及镁离子浓度分布,并通过扫描离子选择性电极实验验证了此模拟方法的可行性.模拟分析表明,当β相离散分布在α相周边时,在与β相相邻的α相区域腐蚀速率最快,形成腐蚀缩颈坑,坑内氯离子富集,进一步加速了α相的腐蚀,最终β相逐渐脱离合金进入溶液;当β相连续分布在α相周边时,α相不断被腐蚀,最终α相全部溶解而只剩β相,求解随即停止.扫描离子选择性电极实验结果表明此模拟模型可以对镁合金的电化学腐蚀进行较好预测和判断.

In combination with a moving mesh technique and a level set function, the corrosion behavior of AZ31 magnesium alloy with a continuous β phase network and the discrete β phase around the a phase in a sodium chloride solution was investigated by finite element method. The distributions of potential and the concentrations of chloride ions and magnesium ions on the interface of magnesium/chloride solution during the corrosion progress were obtained by solving the Nernst-Planck function. The feasibility of this simulation method was validated with scanning ion-selective electrode experiments. Simulation results show that when the β phase is a discrete distribution around the a phase, the corrosion rate of the a phase adjacent to the β phase is the highest, a indented corrosion pit form at this place and chloride ions are enriched, which leads to the acceleration of the corrosion rate of the a phase. Finally, the β phase is removed from the alloy into the solution. However, when the β phase is a continuous distribution around the a phase, the solving process tends to be halted after the a phase is totally dissolved and only the continuous β phase is exposed to the chloride solution. Results of scanning ion-selective electrode experiments indicate that this simulation method can predict the electrochemical corrosion of magnesium alloys well.