| As a kind of light metal material, magnesium alloy has vast applied prospective. For instance, in the fields of automobiles, electronic productions and aerospace, magnesium alloy plays an important role in fuel-efficient environmental protection due to its excellent properties, especially for the current world where resources and energy are declining and the environment is seriously polluted. However, there is still a gap between the real application and development potential of magnesium alloy, which is closely related to its poor corrosion resistance. So far, many efforts have been made regarding to its corrosion prevention with some delightful results, but the corrosion mechanisms have not been understood well, resulting in the failure of magnesium alloy’s industrialization.Consequently, in this study which is served as an elementary step towards enhancing corrosion resistance of magnesium alloys, AM60alloys and rare earth metal Nd were used as raw materials and five groups of AM60+xNd alloys were prepared. The weight-loss tests and electrochemical experiments for the specimens were carried out in the solution of3.5%NaCl, at room temperature. The atmospheric corrosion tests were conducted by exposing the specimens to the open air in Taiyuan City. Several characterization means were employed such as SEM and XRD to characterize the variation of the microstructures of specimens before and after corrosion tests as well as the corrosion products. With the help of the obtained experimental data, the first order function for electrochemical corrosion rate was established and the apparent corrosion rate constant k was calculated. In addition, the effects of grain size, Mg-Al phase, Al11Nd3phase and Nd content on corrosion rate were analyzed based on the characterization and calculation results. Finally, the corrosion behavior of AM60+xNd in3.5%NaCl solutions and the mechanism of element Nd improving the corrosion resistance of AM60alloy were discussed and explored. The acquired experimental data in this study will undoubtedly contribute to the substantial increase in magnesium alloys’corrosion resistance and the expansion of their application fields.Conclusions are as follows:1. In the weight-loss tests, the corrosion rates of alloys with Nd addition obviously decrease and their anti-corrosive property is evidently improved. When the Nd content reaches0.899%, the corrosion rate of AM60alloy decreases by58.2%, from9.43mg·cm-2·d-1to3.95mg·cm-2·d-1. The main corrosion products are Mg(OH)2, Mg6Al2(OH)18·5H2O and a few Mg12Al17·2. In the electrochemical tests, with a trace amount of Nd added into AM60alloys, the substrate electrode potential rises and the corrosion current reduces. Specifically, when Nd content reaches0.899%, the corrosion potential increases from-1.3788V to-1.3327V and the corrosion current decreases from1.913×10-4mA to0.545×10-44mA.3. In the open air corrosion tests, the corrosion condition on the surface of AM60alloy with Nd addition is better that of AM60alloy without Nd addition. Moreover, the AM60+0.899%Nd alloy has the least corroded surface and the best corrosion resistant.4. The dynamic model for corrosion reaction established in line with static weight-loss tests of AM60magnesium alloys shows that the apparent corrosion rate constant k and grain size d of the alloy and the content of Nd is obedient to the function k=0.61nd-1.3and k=0.6exp(-2.7Nd%)+0.58, respectively, where kmax and kmin is1.21μm/h and0.53μm/h, respectively.5. The mechanism of trace element Nd enhancing the corrosion resistance of AM60alloy is as follows:the element Nd refines the grain size and changes the quantities and distributions of β-Mg17Al12and Al11Nd3phases, increasing the electric resistance during the corrosion process and corrosion potential, reducing the corrosion current; The newly formed Al11Nd3phase and the Nd atoms dissolved in the substrate, together change the cloud density around Nd atoms thereby generating a anticorrosion film which is similar to surface coating on the surface as well as the corrosion products, altering the corrosion behavior from pitting to filiform corrosion thereby reducing the corrosion rate. |
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