Research on microstructure and alloy phases of AM50 magnesium alloy

Abstract Comprehensive researches on the microstructure and alloy phases of AM50 magnesium alloy of different status, varying from casting to solid-solution treated and aged ones, were carried out in the present paper. Special attention was drawn to Al–Mn phases and their effects on electrochemical properties of the alloy. The results indicated that Al–Mn phases were the major alloy phases in as-cast, solid-solution treated and aged AM50 alloys. They were quite heat-resistant and almost kept unchanged in terms of morphology, distribution and amount. The majority of Mg 17 Al 12 phase in as-cast alloy could be reduced when the temperature of solid-solution treatment was up to 410 °C and it precipitated as reinforcing phase during aging treatment. According to the microstructure and the corresponding microhardness analysis, it was believed that the strengthening mechanism of AM50 might not be limited to precipitation reinforcement; some other factors such as substructure and re-distribution of alloy elements might play critical roles too. Electrochemical experiments further showed that Al–Mn phases were detrimental to the corrosion resistance of the alloy in question, especially when Al-rich α-Mg and β-Mg 17 Al 12 phases were eliminated.