Evolution of intermetallic phases of Al-Zn-Mg-Cu alloy during heat treatment
(1.黑龙江省哈尔滨市哈尔滨工业大学分析测试中心
2.Analysis and Measurement Center, Harbin Institute of Technology, Harbin 150001, China
3.Northeast Light Alloy Co Ltd, Harbin 150060, China)
2.Analysis and Measurement Center, Harbin Institute of Technology, Harbin 150001, China
3.Northeast Light Alloy Co Ltd, Harbin 150060, China)
Abstract: Al-Zn-Mg-Cu alloy is a favorable choice for aerospace applications requiring good combination of strength and toughness, which is greatly influenced by the coarse intermetallic particles. The evolution of intermetallic particles in an Al-Zn-Mg-Cu alloy during heat treatment was studied by field emission gun scanning electron microscopy (FEG-SEM) and X-ray diffractometry(XRD). The results show that there are lamellar eutectic structure (α(Al)+Mg(Zn,Al,Cu)2) and Al7Cu2Fe particles in the solidified structure. The Al7Cu2Fe particles are embedded in the eutectic structure. The content of eutectic structure decreases with the increase of holding time and disappears after 24 h. The size and morphology of Al7Cu2Fe particles exhibit no change during the heat treatment. It is found that the Al2CuMg phase is formed during the treatment at 460 ℃. A transformation process from the primary eutectic phase Mg(Zn,Al,Cu)2 to Al2CuMg is observed, and the transformation mechanism and kinetics are analyzed. The Al2CuMg constituents form in the primary Mg(Zn,Al,Cu)2 phase, and grow along the eutectic microstructure.
Key words: Al-Zn-Mg-Cu alloy; eutectic structure; intermetallic particles; phase transformation