| Research on surface anti-corrosion is an important aspect of the application of magnesium alloy in the present. Electroless composite plating is a commonly and widely used because of its low cost, simple process, uniform coating thickness. In this paper, Ni-P-Al2O3 composite plate is studied, factors which affect the properties of the composite coating are analyzed, and then the rule of them is summarized under ultrasonic wave vibration.The confirmatory test shows that the chemical composite coating from the ultrasonic process is aignificantly more uniform, dense and more grain refinement than from the traditional process. Besides, the reaction is more intense and the sedimentation is fasterBy using ultrasouic in the chemical coating, the hardness, corrosion resistance and coating rate of the coating are rising with the increasing of the untrasonic power and temperature. When these properties reache to a maximum point, they begin to fall. Therefore, appropriately increasing the unltrasonic power can help to improve the performance, but the power can not rise over from a appropriate level. The coating corrosion resistance and hardness value are reduced first and then rising with the increasing of its power, and reaching the maximum when the power of ultrasonic was 60W and the temperature was 60℃, the dropping tine is 368seconds and the hardness value reached to 439 HV. The dropping time was prolonged 116 seconds, the hardness value could increased above 282HV. The composite coating is amorphous structure of metastable state and the amorphous structure change partially to crystallization after heat treatment at 200℃,at the same time corrosion resistance and coating adhesion achieve the best combination of strength. Intermetallic compounds, such as Ni3P phase, Ni5P2 phase and Ni phase, are precipitated at 300℃.After heat treatment at 400℃,Grain grow up together, coating is completely crystallized,and the performance variation and crystal defects increase. |
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