Effect Of Lanthanum And Cerium Mischmetal On Corrosion Resistance Of AM60B Magnesium Alloy

Magnesium alloys are currently used in industry of the lightest metal structural materials and functional materials for special purposes. They have good performance of thermal and electrical conductivity, damping properties, electro-magnetic screen effect, machinability, castability and easy recycling. Therefore, the magnesium alloy is widely used in the automotive industry, defense industry,3C industry and medical fields. However, the corrosion resistance of magnesium alloys has largely limited its development.In this paper, by adding the mixed rare earth La and Ce to improve the corrosion resistance of AM60B magnesium alloy, and studied the corrosion resistance of AM60B and AM60B-MM magnesium alloys in the solution and the simulated atmospheric.Metallographic analysis indicate that AM60B-MM magnesium alloy formed acicular Al2Ce and Al11La3rare earth intermetallic compound. Reticulated P-Mg17Al12phase continuously distributed in the grain boundaries and the matrix of AM60B, however, in the AM60B-MM, the β-Mg17Al12phase is not continuous distribution, even dispersed in the matrix. The cast microstructure of AM60B-MM magnesium alloy is refined, and the grain becomes smaller.AM60B-MM magnesium alloy was immersed in0.35%NaCl solution for30days, it is formed the composite oxide film of Mg (OH)2, Al (OH)3, MgO, MgAl2O4and CeO2, La2O3on the surface, layer reduced the effective area of the anodic reaction and improved the resistance to localized corrosion. In the hydrogen evolution experiments for100hours, the corrosion current density of AM60B magnesium alloy is0.15x10-6A·cm-2, and AM60B-MM is0.09×10-6A·cm-2which effectively suppresses hydrogen evolution corrosion. Electrochemical testing results under0.35%NaCl solution shows that after adding mixed rare earth, the corrosion current density is smaller, capacitive reactance arc, the impedance modulus and phase angle are bigger, the frequency range peak is broader, the Rsurf and Rct are bigger, CPEsurf and CPEdl are smaller, and the corrosion resistant performance is better.Friction coefficient of AM60B-MM alloy is lower than AM60B alloy, specific wear rate decreased, improving the tribological properties. Under0.35%NaCl solution in the low-load, sliding velocity and short distance, two kind of the magnesium alloys both shows oxidation wear characteristics.Indoor simulation experiments shows that aggressiveness of the salt is NaCl> Na2SO4> NaNO3. When the deposition is more than0.5μmcm-2, the corrosion weight gain increases, the corrosion process intensifies, with the addition of NaCl, AM60B and AM60B-MM alloy follow exponential kinetic equation are:△WNaci=0.349×t0.692and△wNaCl=0.256×t0742.