Study On The Electrodedosition Of Aluminum-Manganese Alloy On Rare-earth Magnet Materials From Ionic Liguid

Magnetic materials have been widely applied in communication, electronics, computers and automotive sectors, however they have poor corrosion resistance in common. Therefore, it is very important to improve the corrosion resistance of NdFeB and TbDyFe.Al-Mn coatings were electrodeposited on sintered NdFeB permanent magnet and TbDyFe(Terfenol-D) in ionic liquid at room temperature.Al-Mn coatings were electrodeposited on sintered NdFeB permanent magnet in MnCl2-AlCl3-EMIC(chloride-1-ethyl-3-methylim-idazolium chloride) ionic liquid at room temperature. The results showed that the amorphous structure of the deposits was obtained at the current density of6mA/cm2, while higher current densities resulted in a mixed structure of amorphous and crystalline. The Al-Mn coating showed excellent adhesion strength on NdFeB substrate with the thermal shock test over30cycles and Lc>80N. The hardness of Al-Mn coating was up to5.4GPa. The amorphous Al-Mn coating showed an anodic sacrificial protection with a low corrosion rate for NdFeB. Meanwhile, the magnetic properties measured by an AMT-4magnetic measurement device showed that Al-Mn coating did not deteriorate the magnetic property of NdFeB.Heat treatment was used to study the influence on the structure and properties of Al-Mn alloy coating electrodeposited on NdFeB substrate. The results showed that: the crystallization temperature of Al-Mn alloy coatings was265-292℃. After heat treatment, the coating maintained completed morphology with no crack on macro perspective, but long straight cracks and intergranular cracks appeared on micro perspective. With the temperature rising, the structure of Al-Mn coating gradually transformed from amorphous into crystalline Al6Mn. The hardness of Al-Mn coating rose along with the increasement of heat temperature. Al-Mn coatings with different phase structures possessed relatively good corrosion resistance, and heat treatment had little imfact on the corrosion resistance of Al-Mn. Wherein the Al-Mn amorphous coating had most excellent corrosion resistance.A preliminary study on electrodeposition amorphouAl-Mn coating on TbDyFe substrate was carried out in AlCl3-EMIC-MnCl2room temperature ionic liquids. The results showed that:After anode etching in AlCl3-EMIC(2:1molar ratio) ionic liquids at the anode current density20mA/cm2for20min, the surface oxide film of the substrate was removed effectively to obtain excellent adhesion strength coating on TbDyFe substrate. Then amorphous structure of Al-Mn coating was obtained at the current density of6mA/cm2in AlCl3-EMIC-MnCl2. The corrosion potential of Al-Mn was lower than that of TbDyFe, so Al-Mn coating showed an anodic sacrificial protection with a low corrosion rate for TbDyFe. Meanwhile Al-Mn coating did not deteriorate the magnetic property of TbDyFe.