Microstructure, Corrosion And Wear Properties Of Al And AlN/Al Coatings On Magnesium Alloy

On account of many advantageous properties such as high strength-to-weight ratio, good electromagnetic shielding characteristics and recyclability, magnesium and magnesium alloy are widely used in aerospace, automotive and other industries. However, the application of magnesium alloy development is restricted by its poor corrosion and wear resistance. One of the important ways to improve the properties of magnesium alloy is attracts surface modification. Among the techniques, the aluminium coatings attracts much attention due to its advantages of high corrosion resistance, good mutual solubility with magnesium substrate and recyclability etc.Al and AlN/Al coating were prepared on magnesium alloy substrate using pulsed bias magnetron sputtering in this study. Effects of the process paprameters such as alloying temperaturer, bias voltage and nitrogen partial pressure etc. on microstructure and properties of the coatings were investigated. Optical microscope (OM), glow discharge spectrometry (GDOES) and X-ray diffraction (XRD) were used to characterize the microstructure and composition of the coatings. Microhardness tester for hardness measurement, ball-on-disc test for tribology performance study, white light interferometer for wear volume measurement, and electrochemical polarization for corrosion resistance test were used.The results show that the Al coatings are composed of an aluminium deposition layer and a diffusion layer. With the increasing of alloyed temperature, the thichness of deposition layer reduces and that of diffusion layer increases. XRD analysis shows that coatings are mainly composed of Al and Mg phase. A small amount of Al12Mg17 phase is appeared at higher temperature of 450℃. Hardness of the coatings gradually decreases along the depth of aluminized coatings. The coatings thickness increases and the hardness gradient becomes smooth with the increasing of alloying temperature. By deposition of Al coatings on magnesium alloy using magnetron sputtering at different alloying temperature, the wear resistance improvement of magnesium alloy is not obvious while the corrosion resistance is raised considerably with increase corrosion potencial of 300mV and an order of magnitude decrease of the corrosion rate. The coating prepared using a bias voltage of 400V shows the best corrosion resistance. The corrosion rate is three orders of magnitude less than that of the magnesium alloy substrate.Based on above aluminizing coatings, AlN/Al mutilayer coating was deposited on magnetron alloy substrate using bias pulsed magnetron sputtering in the nitrogen atomosphere. The XRD analysis results show that AlN phase and Al12Mg17 phase appear in the coating. The wear rate of AlN/Al coated magnesium alloy is decreased one order of magnitude than that of substrate. The corrosion rate of AlN/Al coating prepared in nitrogen partial pressure of 0.4Pa is three orders of magnitude less than the magnesium alloy substrate.