Effects Of Ageing Treatment On Microstucture And Tensil Properties Of Mg-10Gd-3Y-0.6Zr Alloy

Magnesium alloys are said to be one type of green engineering materials in21st century, because of its important using value and widespread application prospect in the areas of aerospace, automobile industry and3C products. In recent years, the magnesium alloys have become more and more attractive to the researchers.As one type of typical magnesium alloys, Mg-10Gd-3Y-0.6Zr alloy has high mechanical properties and good corrosion resistance. The mechanical properties of as-extruded Mg-10Gd-3Y-0.6Zr alloy can be improved by the heat treatment due to the high solid solubility of rare earth elements in the matrix. Therefore, the study will focus on the improvement of mechanical properties for Mg-10Gd-3Y-0.6Zr alloy with different kinds of ageing treatment; on the other hand, with the purpose of supplying theoretical principle for the research, the strengthening mechanism and fracture modes are investigated.The results indicated that the tensile strength decreased with the increase of ageing temperature, but the elongation increased at the same time. That was attributed to the change of size and number of precipitates which formed on the grain boundaries and inside the grains. Otherwise, the fracture modes were decided by the dimension and continuity of grain boundary precipitates.Furthermore, the influences of solution treatment (T4), solution-ageing treatment (T6) and stress induced ageing (SIA) on the microstructure and tensile properties of as-extruded Mg-10Gd-3Y-0.6Zr alloys were different. The elongation was improved since the primary phases were dissolved into the matrix by the T4(490℃/1h) treatment, which induced the decrease of the tensile strength because of the reduction of the stress concentration. As the precipitates formed preferentially on the grain boundaries after T6(490℃/1h-200℃/72h) treatment, the alloy fractured before yielding. The tensile strength was improved by the SIA treatment at250℃, but the elongation decreased. The proper condition of SIA treatment was150MPa/250℃/6h(UTS:390MPa, YTS:342MPa, El:3.2%).