High-temperature Mechanical Properties Of Al-5.5Cu-0.9Mg-0.2Sc-0.15Zr(-xTi) Aluminum Alloys

Through performing the tensile test,low-cycle fatigue test,creep test,microstructure analysis and X-ray diffraction analysis as well as the observations with scanning electron microscope and transmission electron microscope,the effect of Ti element on both microstructure and high temperature tensile properties of extruded Al-5.5Cu-0.9Mg-0.2Sc-0.15Zr alloy subjected to T6 treatment as well as the low-cycle fatigue properties and creep properties of the Al-5.5Cu-0.9Mg-0.2Sc-0.15Zr-1.0Ti alloy at 200? has been investigated in order to provide the theoretical basis for the engineering application of aluminum alloy.The results of microstructural observation show that the Al₃Ti phase forms and the microstructure of Al-5.5Cu-0.9Mg-0.2Sc-0.15Zr alloy will be refined due to the addition of Ti element.The results of X-ray diffraction analysis show that the precipitation phases in the Al-5.5Cu-0.9Mg-0.2Sc-0.15Zr?-xTi?alloys are mainly Al₂CuMg phase and Al₃Ti phase.The results of tensile tests show that with increasing the testing temperature,the ultimate tensile strength and yield strength of Al-5.5Cu-0.9Mg-0.2Sc-0.15Zr?-xTi?alloys decrease while the elongation to failure shows an increase trend.The ultimate tensile strength and yield strength of the 1.0Ti-containing alloy are the highest and those of the 1.5Ti-containing alloy are followed,while the elongation of the 1.0Ti-containing alloy is the highest and that of the1.5Ti-containing alloy is the lowest.The tensile fracture mode for the Al-5.5Cu-0.9Mg-0.2Sc-0.15Zr?-x Ti?alloys is all ductile fracture.The results of low-cycle fatigue test show that the cyclic softening occurs during the fatigue deformation of Al-5.5Cu-0.9Mg-0.2Sc-0.15Zr-1.0Ti alloy at 200?,and a linear relationship between the plastic strain amplitude,elastic strain amplitude and reversals to failure can be noted,which follows the Coffin-Manson formula and the Basquin formula respectively.The fatigue cracks initiate transgranularly at the surface of fatigue samples and propagate in a transgranular mode.The results of creep test reveal that in the stress range from 180MPa to 210MPa and at200?,the creep rate of Al-5.5Cu-0.9Mg-0.2Sc-0.15Zr-1.0Ti alloy is in the range from 10^-9s^-11 to 10^-8s^-1 and the creep stress exponents is about 16.78.With increasing the stress,the creep life of the alloy decreases and the steady creep rate increases.In addition,the creep deformation mechanism of Al-5.5Cu-0.9Mg-0.2Sc-0.15Zr-1.0Ti alloy is the dislocation climbing mechanism controlled by the second phase.The creep fracture occurs in a transgranular manner and the typical ductile fracture characteristics can be noted.