Study On Corrosion And Mechanical Properties Of Magnesium Alloy Containing CuAZ91

AZ91-xCu（0,0.5,1,2）series alloy with different Cu content has been prepared with vacuum melting furnace,these alloy samples had been treated with solid solution and aging.The results of the test analysis can provide a reference for further development of soluble magnesium alloys in the future.Their phase composition and microstructures were characterized by X-ray diffraction（XRD）and scanning electron microscope with energy dispersed X-ray（SEM/EDX）,their mechanical properties were tested with universal material testing machine,and their corrosion properties were tested with mass loss in immersion testing and electrochemiscal polarization curve testing method.The main research content and results are as follows:（1）AZ91 magnesium alloy is mainly composed ofα-Mg andβ-Mg₁₇Al₁₂phases.The addition of Cu will cause the Mg₂Cu and Cu₅Zn₈phases to appear in the alloy.In the as-cast AZ91-xCu alloy,the hardness of the alloy increases with the Cu content increasing.The hardness of AZ91-2Cu alloy is 65.9HV,which is 15.4%higher than that of AZ91 alloy.Adding Cu to the AZ91 magnesium alloy improves the tensile strength of the magnesium alloy,but the tensile strength and elongation of AZ91-2Cu are lower than that of AZ91-1Cu alloy.The tensile strength of AZ91-1Cu alloy is 180MPa and the elongation is 13.74%.（2）With the Cu content and temperature increasing,the corrosion rate of the alloy increases,the corrosion rate of as-cast AZ91-2Cu alloy is 22.70mg/（cm²h）when testing in 3.5%（wt）NaCl solution at 90℃,which is 425%higher than that of AZ91alloy at the same temperature.The polarization curve test shows that with the Cu content increasing,the corrosion potential of the alloy decreases,and the corrosion resistance capability of the alloy decreases,which showing the same law as weight loss testing with immersion method.The as cast AZ91-xCu alloy has been solid solution-treated at 400℃ for 12 hours.Theβ-Mg₁₇Al₁₂phase continuous network with continuous network shape in the alloy gradually dissolves into the matrix,which increases the Al content in the alloy matrix.The grain boundary of the solid solution alloy is obvious,and the grain size is larger than that of the as-cast alloy,and the second phase containing Cu have no obvious changes with that in the as-cast alloy.However,in the AZ91-2Cu alloy,due to the increase of Al content in the alloy matrix and a higher Cu content,the Al₂Cu phase appears.After the solution treatment,the solid solution strengthening effect due to the increase of the Al and Cu content in the alloy matrix has been abated by the hard and brittleβ-Mg₁₇Al₁₂phase in the alloy being dissolved into the matrix,so the hardness of the solid solution alloy does not change much compared to that of the as-cast alloy.The tensile strength of AZ91-2Cu in solid solution is 200MPa,which is 11.11% higher than the ultimate tensile strength of as-cast alloy,but the ultimate elongation of solid solution alloy is 14.13%of AZ91-1Cu.In 3.5% NaCl solution at 90℃,the corrosion rates of the solid solution treated AZ91-1Cu and AZ91-2Cu alloys are 11.55mg/（cm²h）and 27.31 mg/（cm²h）respectively.The corrosion rate of the solid solution treated AZ91-2Cu alloy is higher20.31%than that of the as-cast AZ91-2Cu.（3）The solution-treated AZ91-xCu alloy is aged at 200℃℃ for 6 hours.After aging treatment,the metallographic microstructure of the AZ91-xCu alloy has no obvious change compared with that of the solid solution treated AZ91-xCu alloy,but theβ-Mg₁₇Al₁₂phase content in the matrix increases.The hardness of the aging alloy is greatly improved compared to that of the as-cast state due to the increase of solid solution strengthening andβ-Mg₁₇Al₁₂precipitation phase strengthening,and the hardness increases with the increase of Cu content in the alloy.The hardness of the aging treated AZ91-2Cu alloy reaches 81.4HV,which is 23.5%higher than that of as-cast alloy.The tensile strength of the aged AZ91-2Cu alloy is lower than that of AZ91-1Cu.The corrosion rate of the aged alloy is lower than that of the solid solution alloy due to the increase ofβ-Mg₁₇Al₁₂precipitation phase in aging process.The corrosion rate of the aged AZ91-2Cu alloy is 18.32mg/（cm²h）in 3.5%NaCl solution at 90℃,which is 32.9%and 19.30%lower than that of the solid solution alloy and the as cast alloy respectively.