摘要
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.
采用SEM、TEM、EDS、DSC、XRD和拉伸实验研究铸态7X50合金及其均匀化处理过程的组织演变。结果表明,铸态7X50合金相组成主要有S(Al2CuMg)、T(Al2Mg3Zn3)、Mg Zn2和少量的Al7Cu2Fe和Al3Zr相。均匀化处理过程中枝晶网和残留相逐渐减少,经(470°C,24 h)+(482°C,12 h)均匀化处理时,T相消失,S相有微量残留,Al7Cu2Fe相几乎没有变化。铸态合金的DSC曲线中在477.8°C处有一较强吸热峰,经470°C、1 h均匀化后合金的DSC曲线在487.5°C处出现一个新的吸热峰,而经482°C、24 h均匀化处理后合金在487.5°C处的吸热峰基本消失。在XRD谱中未出现T(Al2Mg3Zn3)相,这和T相与S(Al2CuMg)及Mg Zn2相相关的结论相吻合。预均匀化处理制备的板材中再结晶晶粒分数明显降低,抗拉强度和断裂韧性相对常规均匀化处理制备的板材分别提高约15 MPa和3.3 MPa·m1/2。
基金
Project(2011KJZX1-2)supported by the Science and Technology Development Fund of Aluminum Corporation of China
