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Study on Properties of Magnetron Sputtering SiN Film on AZ31 Magnesium Alloys

Author: LuoXianSheng
Tutor: HuangJiaMu
School: Chongqing University
Course: Materials Science
Keywords: magnetron sputtering AZ31 magnesium alloy corrosion resistance SiNx film adhesive strength
CLC: TG174.4
Type: Master's thesis
Year: 2009
Downloads: 135
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Abstract


Magnesium alloy is the lightest metal structure material of the practical application material, with excellent properties,such as low density, high specific strength and stiffness, with good shock absorption ability, electromagnetic shielding ability, etc.. Widely used in the automotive industry, aerospace industry and microelectronics and many other fields. However, its poor corrosion resistance have hindered the wider use of magnesium alloy. At present the surface treatment used for magnesium alloy are:chemical conversion coating, anodicoxidation treatment, chemical plating and so on. Magnetron sputtering is the main method for the industrial application of film owing to its high deposition rate , simple process, good film quality and environmentally friendly. SiNx thin film was deposited on AZ31 magnesium alloy by magnetron sputtering method.Scanning electron microscope(SEM),X-ray diffraction and X-ray photoelectron spectroscopy were used to investigate the surface morphology,crystalline structure and chemical composition of the film and the impact of processing parameters on the corrosion resistance of the SiNx film. Deposit the Al, Zr, Ti metal film to improve the adhesive power between SiNx film and magnesium alloy.Immersion test and electrochemical test were used to research corrosion resistance of the composite film, cross cut test was used to evaluate the adhesive strength between film and magnesium alloy.It was found that the SiNx film was amorphous and nitride-rich. Its surface was smooth and dense ,there are no pinholes defects exist. The processing parameters impact thickness and quality of SiNx film.The SiNx film cracking and poor adhesion strength property because of its internal stress and loss of protective effect of magnesium alloy.There were pinholes defects exist in the metal film and the size of the defects were almost 10~20μm diameter. The densest metal film is Zr film, the number of pinholes defects in Al film has the largest number of pinholes. Immersion tests and electrochemical tests showed that the metal film can improve corrosion resistance of magnesium alloy.The cross cut test showed that the adhesive strength between Zr-SiNx, Ti-SiNx composite film and magnesium alloy have reached one degree and the Al-SiNx composite film has reached two degrees. Electrochemical tests showed that the corrosion current density of the sample deposite Zr-SiNx film was decreased three orders of magnitude than bare AZ31 magnesium alloy and in the anodic polarization areas ,the corrosion current density increased slowly with increase the voltage. The free corrosion potential of the sample deposite Ti-SiNx film higher about 300mv than bare AZ31 magnesium alloy and the corrosion current density was decreased three orders.About 100mv passive area appeared when the working potential was negative -1.152V. The corrosion resistance of the sample deposite composite film was better than the sample deposite metal film.The metal film can improve the adhesive strength between film and magnesium alloy matrix and improve the corrosion resistance of composite film.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology
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