The evolution of the eutectic structures in the as-cast and homogenized 7X50 aluminum alloys was studied by scanning electron microscopy(SEM), transmission electron microscopy(TEM), energy dispersive spectrometer(EDS)...The evolution of the eutectic structures in the as-cast and homogenized 7X50 aluminum alloys was studied by scanning electron microscopy(SEM), transmission electron microscopy(TEM), energy dispersive spectrometer(EDS), differential scanning calorimetry(DSC), X-ray diffraction(XRD) and tensile test. The results show that the main phases are S(Al2CuMg), T(Al2Mg3Zn3) and Mg Zn2, with a small amount of Al7Cu2 Fe and Al3 Zr in the as-cast 7X50 alloy. The volume fraction of the dendritic-network structure and residual phase decreases gradually during the homogenization. After homogenization at 470 °C for 24 h and then 482 °C for 12 h, the T(Al2Mg3Zn3) phase disappears and minimal S(Al2CuMg) phase remains, while almost no change has happened for Al7Cu2 Fe. There is a strong endothermic peak at 477.8 °C in the DSC curve of as-cast alloy. A new endothermic peak appears at 487.5 °C for the sample homogenized at 470 °C for 1 h. However, this endothermic peak disappears after being homogenized at 482 °C for 24 h. The T(Al2Mg3Zn3) phase cannot be observed by XRD, which is consistent with that T phase is the associated one of S(Al2CuMg) phase and Mg Zn2 phase. The volume fraction of recrystallized grains is substantially less in the plate with pre-homogenization treatment. The strength and fracture toughness of the plate with pre-homogenization treatment are about 15 MPa and 3.3 MPa·m1/2 higher than those of the material with conventional homogenization treatment.展开更多
基金Project(2011KJZX1-2)supported by the Science and Technology Development Fund of Aluminum Corporation of China
文摘The evolution of the eutectic structures in the as-cast and homogenized 7X50 aluminum alloys was studied by scanning electron microscopy(SEM), transmission electron microscopy(TEM), energy dispersive spectrometer(EDS), differential scanning calorimetry(DSC), X-ray diffraction(XRD) and tensile test. The results show that the main phases are S(Al2CuMg), T(Al2Mg3Zn3) and Mg Zn2, with a small amount of Al7Cu2 Fe and Al3 Zr in the as-cast 7X50 alloy. The volume fraction of the dendritic-network structure and residual phase decreases gradually during the homogenization. After homogenization at 470 °C for 24 h and then 482 °C for 12 h, the T(Al2Mg3Zn3) phase disappears and minimal S(Al2CuMg) phase remains, while almost no change has happened for Al7Cu2 Fe. There is a strong endothermic peak at 477.8 °C in the DSC curve of as-cast alloy. A new endothermic peak appears at 487.5 °C for the sample homogenized at 470 °C for 1 h. However, this endothermic peak disappears after being homogenized at 482 °C for 24 h. The T(Al2Mg3Zn3) phase cannot be observed by XRD, which is consistent with that T phase is the associated one of S(Al2CuMg) phase and Mg Zn2 phase. The volume fraction of recrystallized grains is substantially less in the plate with pre-homogenization treatment. The strength and fracture toughness of the plate with pre-homogenization treatment are about 15 MPa and 3.3 MPa·m1/2 higher than those of the material with conventional homogenization treatment.
