Intermetallic phase formation and evolution during homogenization and solution in Al-Zn-Mg-Cu alloys

• Published in: Science China. Technological sciences 2013-11, Vol.56 (11), p.2827-2838
• Main Authors: Li, ChunMei, Chen, ZhiQian, Zeng, SuMin, Cheng, NanPu, Chen, TianXiao
• Format: Article
• Language: English
• Subjects: Al-Zn-Mg-Cu系合金; Alloys; ALUMINUM ALLOYS (50 TO 99 AL); Aluminum base alloys; Engineering; Evolution; HEAT TREATING; Homogenization; Homogenizing; INTERMETALLIC COMPOUNDS; Intermetallic phases; Magnesium; PHASES; Solution heat treatment; X-射线衍射仪; 同质化; 固溶化处理; 差示扫描量热法; 扫描电子显微镜; 演化; 金属间相
• ISSN: 1674-7321; 1869-1900
• DOI: 10.1007/s11431-013-5356-5

The effects of major alloy element contents of Zn, Mg, Cu in Al-Zn-Mg-Cu alloys on the formation and evolution of intermetallic phases during casting, homogenization and solution treatment have been investigated through using X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. Experimental results showed that a relatively higher Zn content with lower Mg and Cu contents was beneficial to the formation of MgZn2 phase instead of the A12CuMg phase, which resulted in the unicity of the intermetallics in the A1 matrix, and that the MgZn2 phase was easier for diffusion and dissolution during homogenization and solution than the Al2CuMg phase. Additionally, the results of the first-principles calculations gave support for explaining the experimental phenomena. A larger absolute value of formation enthalpy and a smaller value of binding energy of the MgZn2 phase, as compared with the Al2CuMg phase, give it priority to precipitate during casting and make it easier to re-dissolve during homogenization and solution treatment. What＇s more, higher elastic constants with severe anisotropy of Young＇s modulus make undissolved blocks of AI~CuMg phase act as crack initiation, which degrade the perfor- mance of the materials.