Investigation On Corrosion Characteristic And Morphology Of Ce-rich Sintered Magnet Prepared By Double Main Phase Method

NdFeB magnets, with remarkable magnetic properties, are widely used in many fields. Nevertheless, on one hand, the price of NdFeB made by traditional sintered method is pretty high. On the other hand, with the exploitation of Nd and Pr, the other rare earth elements are seriously wasted seriously, which leads to very low comprehensive utilization of rare earth resources. Recently, double main phase sintering process, with its low cost and high utilization of rare earth resource, has been gradually promoted. However, few researches have been made to study the corrosion behavior and mechanism of the double main phase sintered magnets. On this basis, the corrosion behavior, the corrosion product composition, mechanism of magnets prepared by the double main phase sintering process had been studied for the first time by comparing with N45 magnets which were prepared by traditional sintering method. The main contents of this paper are as follows:The corrosion behavior of rich-Ce sintered magnet has been investigated in hygrothermal environment, and microstructure of magnet, the weight loss and surface topography of corroded magnets have been obtained. And a kind of common commercial magnet N45 with properties similar to rich-Ce magnet was comparatively investigated. Results shows that the weight loss of rich-Ce sintered magnet is lower than that of N45 magnet, the corrosion depth is shallower, and the adhesion property of corrosion products is greater. The corrosion mechanism of rich-Ce sintered magnets and N45 magnets are the same. Corrosion of two kinds of magnets both start from the rare earth phase. The corrosion products of rich-Ce sintered magnet are Fe2O3、Fe3O、γ-FeOOH、Nd2O3、Ce2O3, ect.The electrochemical corrosion behavior of rich-Ce sintered magnet and N45 magnet were studied in three different solutions,3.5 wt.% NaCl,1.1 wt.% NaH2PO4, and 2.5 wt.% NaOH solution. It is found that in the three solutions, the corrosion current of rich-Ce sintered magnet is less than that of N45 magnet. The corrosion current is an important indicator to measure the corrosion resistance of materials. The smaller the corrosion current is, the better the corrosion resistance is. So the anti-corrosion property of rich-Ce sintered magnet is better than that of N45 magnet. Besides, it was found that magnets revealed the best anti-corrosion property in 2.5 wt.% NaOH solution, while the worst in 3.5 wt.% NaCl solution.The magnets which were prepared by double main phase sintering process were experimented in HAST. The morphology of (Ce2oNd8o)31Feba1B1M1 magnet corroded under humid and hot conditions was studided. The morphology of the corrosion products was bobbles-like and ball-like. The bobbles-like products was mainly composed of grain boundary corrosion products, which was rare earth oxide, while the ball-like products was iron oxide. Finally, the mass loss of (Ce2oNdgo)31Feba1B1M1 magnets was analyzed.