Study Of Preparation Of Aluminium Alloying Coating On The Surfaces Of Magnesium And Its Alloy By Molten Salt Modification

As the lightest structural metallic material, magnesium alloy is widely used in a number of areas such as automobile and aerospace industry because of its excellent properties, but the poor corrosion resistance, wear resistance and creep property restrict its expansive application. In recent years, increasing interest has been given to the surface modification of magnesium alloy in order to enhance its corrosion and wear resistance.Referenced on other surface modification technologies, molten salt diffusion treatment is presented in this paper which has comparative advantages such as low temperature, low cost, easy to operate. Magnesium and aluminium intermetallic compound coating can be prepared on the surface of magnesium alloy and it can greatly enhance the corrosion resistance of magnesium alloy. The research and conclusions are below:Molten salt diffusion treatment was taken on the surface of magnesium and AZ91D magnesium alloy with AlCl3-NaCl system. Different treatment temperature and time were taken to analyze the influencing factors. We could get thicker alloying layer with better corrosion resistance by higher treatment temperature and longer time,but the compactness and corrosion resistance would decrease if the temperature was too high. The cross-section morphology of the layer was observed with optical microscope and the microstructure was observed with scanning electron microscope (SEM). The layer showed good connection with Magnesium alloy and the thickness was between 10-30μm. The alloying layer on mg surface was mainly consisted of Mg, Mg17Al12,ε-MgAl andβ-MgAl based on XRD analysis. The electrochemical tests in 3.5wt% NaCl, including electrode potential and time test, alternating current impedance analysis and polarization curve, indicated that the treated ones showed higher electrode potential and impedance compared to untreated Magnesium alloy. The layer could decrease the corrosion rate so as to enhance the corrosion resistance of Magnesium alloy. The crack formed in the coating at high temperature could decrease the corrosion resistance of magnesium alloy. The proper treatment temperature was about 300℃. Diffusion was the leading process during the formation of the alloying layer.