Effect of homogenization treatment on microstructure and mechanical properties of DC cast 7X50 aluminum alloy
(1. Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education,
Northeastern University, Shenyang 110004, China;
2. Northeast Light Alloy Co., Ltd., Harbin 150060, China;
3. School of Materials Science and Engineering, Central South University, Changsha 410083, China)
Northeastern University, Shenyang 110004, China;
2. Northeast Light Alloy Co., Ltd., Harbin 150060, China;
3. School of Materials Science and Engineering, Central South University, Changsha 410083, China)
Abstract: 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 MgZn2, with a small amount of Al7Cu2Fe and Al3Zr 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 Al7Cu2Fe. 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 MgZn2 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.
Key words: 7X50 aluminum alloy; microstructural evolution; homogenization; residual phase; recrystallization