Effect Of Mischmetal On Corrosion Resistance Of ZM5 Magnesium Alloy

Magnesium alloy is known as the "21st Century Green Engineering material".Enhance the research on corrosion resistance of magnesium and magnesium alloy and actively explore the channel of promoting corrosion resistance of magnesium and magnesium alloy is very useful to promote magnesium alloy's application as structural material and play its performance advantages fully.This paper depend on the basis of the effect of mischmetal on oxidation resistance of ZM5 magnesium alloy and continue to research the effect of mischmetal on corrosion resistance of ZM5 magnesium alloy.In other words,Promoting corrosion resistance of ZM5 magnesium alloy through the way of alloying.Because the technology condition of alloying is simple and easy to realize,it is an ideal channel to promote corrosion resistance of magnesium alloy through the way of adding some appropriate alloying elements. This paper analyze the different content of mischmetal elements addition on the impact of microstructure of ZM5 magnesium alloy.The effect of mischmetal on corrosion behavior of ZM5 magnesium alloy was studied in 3.5% NaCl solution,and the corrosion mechanism was discussed.The influence of mischmetal elements on the microstructure and phase of ZM5 alloy was investgated by optical microscope(OM),scanning electron microscope (SEM),energy spectrum analysis(EDS) and X-ray diffract analyzer(XRD).The experimental results showed that,the appropriate addition of mischmetal can refine the casting microstructure of ZM5 alloy and make the discontinuously distributed and reticularβ-Mg₁₇Al₁₂ phase broken,dispersed and well-distributed in the matrix. Two additional types of phases,Al3Ce phase and Al11La3 phase are observed in grain boundary. In the present work, 0.1wt%RE added to ZM5 could gain the best refinement effect.When solution treatment was carried out for 12h at 405℃,β-Mg₁₇Al₁₂ phase dissolve intoα-Mg matix. Theβ-Mg₁₇Al₁₂ phase separated out fromα-Mg matix again when ageing treatment was carried out for 8h at 200℃.The corrosion behavior of ZM5-xRE magnesium alloy in 3.5% NaCl solution was investgated by static weight-loss test and polarization curve measurement,scanning electron microscope(SEM),energy spectrum analysis(EDS) and X-ray diffract analyzer(XRD).The experimental results showed that the appropriate addition of mischmetal is benefit to improve the corrosion resistance,reduce the corrosion rate and minish the corrosion current in evidence.The casting alloy's corrosion resistance was better than the ageing treatment alloy, the solution treatment alloy had the worst corrosion resistance. Whatever,the alloy containing 0.1wt%RE had excellent corrosion performance.The relationship between microstructure and corrosion performance was discussed. The investigation showed that the smaller the grain size and the lower segregation degree of Al, the better corrosion resistance of alloys will have; the more dispersed and well-distributedβ-Mg₁₇Al₁₂ phase in the matrix, its galvanic cathode effect will be lower,the better corrosion resistance of alloys will have.The excess addition of mischmetal would bring down the corrosion resistance of ZM5 alloy.Research on the corrosion product film found:the role of the corrosion product film is established on the basis of the alloy, The casting state corrosion product film on the corrosion inhibition is better than the solid solution state and the ageing state. the solid solution state corrosion product film have the worst corrosion resistance; Once the corrosion product films are damaged, corrosion will be further development, lead to increasing corrosion rate. XRD analysis of the corrosion products showed that the casting state corrosion product were consist of Mg(OH)₂,Mg₂(OH)₃Cl·2H₂O and Mg₃(OH)₅Cl·4H₂O,The heat treatment state corrosion products were consist of Mg(OH)₂,Mg₂(OH)₃Cl·2H₂O,Mg₂(OH)₃Cl·3H₂O,Mg₂(OH)₃Cl·4H₂O and Mg₃(OH) 5Cl·3H₂O.