7449高强韧铝合金均匀化热处理及微观组织演变

Homogenization Treatment and Microstructure of High-Strength and High-Toughness 7449 Aluminum Alloy

利用光学显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、能谱分析(EDS)、差示扫描量热(DSC)、X射线物相分析(XRD)研究了7449高纯高强韧铝合金均匀化热处理制度及其微观组织演变。结果表明:7449合金铸锭组织存在枝晶偏析,Zn,Cu原子沿晶界偏析严重,非平衡共晶相沿晶界呈连续网状分布,共晶相组成为α(Al)+Mg(AlZnCu)2四元相,初始回溶温度为477℃;合金经不同均匀化热处理后,非平衡共晶相发生回溶,且析出弥散分布的Al3Zr粒子。研究了不同的均匀化热处理制度对7449合金微观组织的影响,均匀化热处理温度越高,合金非平衡共晶相回溶效果越好,合金经(440℃/12 h)+(470℃/24 h)均匀化热处理后第二相回溶充分,且析出弥散的Al3Zr粒子,抑制后续加工和固溶处理过程中的再结晶。最终确定合金合理的均匀化热处理制度为(440℃/12 h)+(470℃/24 h)。

The microstructure and homogenization heat treatments of 7449 high-strength and toughness aluminum alloy were investiga- ted by optical microscopy （OM）, scanning electron microscopy with energy dispersive X-ray spectroscopy （SEM-EDX）, transmission electron microscopy （TEM）, differential scanning calorimetry （DSC） and X-ray diffraction analysis （XRD）. The results indicated that the ingot of 7449 aluminum alloy presented a dendritic microstructure with segregation, Zn and Cu atoms segregated along the grain boundary heavily. The phase of nonequilibrium eutectic, ct （A1） ＋ Mg（AIZnCu） 2, distributed along the grain boundary. The overheating temperature of the eutectic phase was 477℃. After various homogenizing treatments, the nonequilibrium eutectic dissolves into the matrix and A13Zr dispersoids precipitated. Various homogenization treatments were studied, which indicated the nonequilibrium eutectic dis- solved more as the temperature increasing. After homogenized at （440℃/12 h） ＋ （470℃/24 h）, the residual second phase dissolved almost completely, and A13Zr particles precipitated diffusedly, which would inhibit the recrystallization in the following process and solu- tion treatments. Finally, （440℃/12 h） ＋ （470℃/24 h） was identified as the reasonable homogenization process of the 7449 alloy.