| Sintered NdFeB magnets are widely used in various fields due to their excellent magnetic properties.However their poor corrosion resistance limits their further applications.At present,the most popular method to improve their corrosion protection ability in industry is coating.In this paper,a pure aluminum(Al)coating was deposited by direct current(DC)magnetron sputtering on the surface of sintered NdFeB magnets and glass slides with different sputtering parameters,respectively,including vacuum degree,deposition pressure,substrate temperature,sputtering power density and rotation speed.The effect of sputtering parameters on the microstructure,adhesion strength and corrosion resistance of the coating was investigated in details.The specific research contents and the conclusions are listed as fol ows:(1)The effects of different sputtering parameters on the morphologies,thickness and crystal orientation of Al coating were investigated.The results showed that the thickness and the density of the Al coating increased upon vacuum degree.The thickness of the Al coating increased,but the density of Al coating decreased with increasing deposition pressure.In addition,the substrate temperature and the rotation speed had an insignificant influence on the film thickness.However,the surface density of AI coating increased with increasing substrate temperature,and the decreasing rotation speed.The thickness of Al coating increased linearly upon the sputtering power density while the density increased initially but then decreased.Moreover,the sputtering parameters had no effect on the crystal orientation of Al coating.(2)The effects of different sputtering parameters on the corrosion protection ability of Al coating was investigated.The corrosion resistance of the magnetron sputtered Al coating increased with increasing the vacuum degree.The Al coating deposited at a lower deposition pressure was more corrosion resistant.Increasing the substrate temperature in a certain range was helpful to the corrosion resistance of coating.A too high or too low sputtering power density was detrimental to the corrosion resistance of the A1 coating.The Al coating deposited at a lower rotation speed presented a better corrosion resistance.In addition,the corrosion behavior of the Al coating deposited on the surface of the NdFeB magnet could be accelerated by the galvanic effect due to the presence of the micro defects in the coating.Thus,the corrosion resistance of the A1 coating deposited on the NdFeB magnet is much lower than that of the Al coating deposited on the glass slide.(3)The effects of different sputtering parameters on the adhesion strength between A1 coating and the substrate NdFeB magnet was investigated.The adhesion strength between the A1 coating and the substrate NdFeB magnet increased first but then decreased with the increase of vacuum degree,deposition pressure,sputtering power density and rotation speed.The decrease in adhesion strength when the vacuum degree further increased could be attributed to excessive internal stress of the film.The increase of substrate temperature adversely affected the adhesion strength of Al coating.The compactness of A1 coating was the primary factor determining the performance of the coating.The adhesion strength between the A1 coating and the substrate NdFeB magnet was also affected by the microstructure.The Al coating fractured within the coating when being peeled off due to the presence of a relatively high density of defects in the coating,while the Al coating could be mainly peeled off along the coating/substrate interface when it contained a relatively low density of coating defects. |
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