Corrosion Resistance Of Mg-9Gd-4Y-1Nd-0.6Zr Alloy And Cerium Conversion Film

Mg-9Gd-4Y-1Nd-0.6Zr alloy was characterized as light, high strength, heat resistant and good deep drawability etc.It is significant for those fields with a strong demand for weight reduction, such as aerospace components, weapon equipments, and communication and transport tools and so on. But bad corrosion resistance of the Mg alloy made it short life and expensive in its application. Only to improve corrosion resistance of the Mg alloy can the Mg alloy industry develop fast. According to this problem, corrosion resistance of Mg-9Gd-4Y-1Nd-0.6Zr alloy in different environments was investigated. To improve the corrosion resistance of Mg-9Gd-4Y-1Nd-0.6Zr alloy, ageing treatment, alloying Ce and cerium conversion film were studied. All were studied systematically by experimental methods such as optical microscopy (OM), scanning electron microscopy (SEM) with energy dispersive X-ray (EDAX), X-ray diffractometer (XRD), Fourier Transform Infrared Spectrometer (FTIR), electrochemical workstation etc. Draw a conclusion as following:(1) To explore the pitting mechanism, the pitting corrosion behavior of Mg-9Gd-4Y-1Nd-0.6Zr alloy was investigated by SEM. The pitting kinetic mode of the Mg alloy was established.The pitting of Mg-9Gd-4Y-1Nd-Zr alloy plate was caused by potential between second phase particles and a-magnesium. The galvanic corrosion occurred in aqueous environment around the coarse second phase particles which riched rare earth in the Mg alloy. The Mg alloy corrosion resistance can be improved by proper heat-treatment or alloying Ce.(2) The effect of ageing treatment on the strength and corrosion resistance of Mg-9Gd-4Y-1Nd-0.6Zr alloy was revealed. The high strength over-aged Mg alloy was related to theβ'andβ1 phase. The over-aged sample at the grain boundaries were decorated with small and discontinuously distributed particles. The corrosion channels were blocked by small particles which distributed discontinuously at grain boundaries.(3) It is found that by adding Ce into Mg-9Gd-4Y-1Nd-0.6Zr alloy, the Mg alloy corrosion rate decreased by the passivation film. It makes not only second phase particles distribute continuously as net which can restrain corrosion, but also refines the Mg alloy grain with addition of Ce. By adding Ce to Mg-9Gd-4Y-1Nd-0.6Zr alloy, corrosion potential moved positive and the passivation current decreased, which indicate that the corrosion resistance of the Mg alloy has been improved. The positive corrosion potential makes oxidation rate constant decrease and dioxidation rate constant increase. With the addition of 0.5% Ce into Mg-9Gd-4Y-1Nd-0.6Zr alloy, the Mg alloy got the optimum corrosion resistance.(4) The optimization of deposition parameters of cerium conversion film was pH 10.0, time 30 min,0.05 M accelerating agent and T 25℃by orthogonal table L (9,34). The effects of corrosion resistance influenced in sequence pH> electrochemical deposition time> concentration of accelerating agent> temperature.(5)Mg-Ce hydrotalcite film on Mg-9Gd-4Y-1Nd-0.6Zr magnesium alloy surface provides better corrosion protection than Ce conversion film. The better corrosion resistance can be attributed to the Mg-Ce hydrotalcite exhibiting Cl" and CO32- anion exchangeability without changing its structure in chloride media. The carbonate anion has been proved to be the preferred anion for intercalation, and once intercalated, it was very hard to exchange with other anions。...