流場環(huán)境中AZ31鎂合金的腐蝕行為研究

流場環(huán)境中AZ31鎂合金的腐蝕行為研究CORROSION BEHAVIOR OF AZ31 MAGNESIUM ALLOY IN DYNAMIC CONDITIONS

采用自主構建的體外模擬流場環(huán)境實驗平臺，通過電化學阻抗譜（EIS）測量、拉伸實驗、模擬體液pH值變化測試、SEM觀察等方法，對AZ31鎂合金在流場環(huán)境中的腐蝕行為進行了研究。從腐蝕電化學角度探究了流場中鎂合金腐蝕速率與流速的定量關系，并采用ANSYS有限元分析研究了流態(tài)與剪切力作用對鎂合金不同部位腐蝕差異的影響。結果表明，流場會加速AZ31鎂合金的腐蝕，在腐蝕初期，腐蝕電流密度icorr與流場平均流速ν之間存在〖i_corr〗^(-1)=〖i_c〗^(-1)+A·ν^(-1/2)的關系，其中，ic為不考慮擴散影響時的腐蝕電流密度，A為常數。腐蝕速率隨流速增加而增大，且隨著腐蝕時間延長，由于腐蝕產物的影響而逐漸偏離icorr-1~ν-1/2的線性關系。有限元分析表明，樣品不同部位表面流體流態(tài)及剪切應力分布不同，局部傳質系數K存在顯著差異，不同流速下試樣邊緣部位的傳質系數是中間的4~5倍，試樣局部腐蝕形貌與剪切應力分布及流態(tài)差異相對應。

Magnesium alloy is now a promising bio-absorbable material. The previous researches on the corrosion and degradation behavior of biomedical magnesium alloy are mainly carried out in static conditions in vitro. However, considering the real physiological flow field of different flow states in vivo, the static degradation experiments can not effectively simulate the real situation. It is important to study the effect of flow field on the corrosion behavior of magnesium alloy and establish the relationship between flow rate and corrosion rate for the research and development of biomedical magnesium alloy. The corrosion behavior of AZ31 magnesium alloy in the flow field was studied using a self-designed dynamic test bench in vitro by electrochemical measurement, tensile method, pH value test of SBF and SEM observation in this work. The relationship between the corrosion rate of magnesium alloy and the flow rate of the flow field was investigated from the perspective of corrosion electrochemistry. The influence of flow state and flow-induced shear stress (FISS) on corrosion behaviors at different positions of magnesium alloy was also studied by ANSYS finite element analysis. The results show that the flow field will accelerate the corrosion of AZ31 magnesium alloy and the corrosion rate increases with the increase of the flow rate. There is a relationship between the corrosion current density icorr of magnesium alloy and the average flow rate ν during the early corrosion stage, namely 〖i_corr〗^(-1)=〖i_c〗^(-1)+A·ν^(-1/2), where ic is the corrosion current density ignoring the influence of diffusion, and A is constant. With the corrosion time extended, due to the influence of the corrosion products, the experimental results gradually deviate from the calculated linear relationship of icorr-1 ~ ν-1/2. Also, there are significant differences in the fluid flow state and FISS distributions at different positions of the sample. The mass transfer coefficient at the edge of the sample of different flow rates is 4 to 5 times that at the middle position. The localized corrosion morphology corresponds well to the FISS distribution and the difference of flow state.

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