采用光学显微镜(OM)、扫描电镜(SEM)、电子探针(EPMA)、波谱分析(WDS)、X射线衍射(XRD)以及差示扫描量热仪(DSC)等技术对Al-Zn-Mg-Cu-Zr-0.12Ce合金铸态组织及均匀化退火过程中的组织演变进行研究.结果表明:该合金铸态组织存在严重的枝晶偏析,主要由α(Al)基体、α(Al)+Mg(Zn,Al,Cu)2非平衡共晶组织以及少量的θ(Al2Cu)相、Al8Cu4Ce相、Al7Cu2Fe相构成;均匀化退火过程中,大量层片状共晶组织溶入基体,同时转变生成Al2CuMg相;合金的过烧温度为474.87℃;合金的最佳单级均匀化退火工艺为465℃、40 h,这与均匀化动力学方程测算结果接近;合金经(435℃,8 h)+(470℃,32 h)双级均匀化退火处理后,回溶效果更好,主要残留相为难溶的Al2CuMg相,少量含Fe杂质相以及Al8Cu4Ce相.
The microstructure of the as-cast Al-Zn-Mg-Cu-Zr-0.12Ce aluminum alloy and microstructure evolution during homogenization were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), electron probe micro-analyzer (EPMA), wavelength dispersive spectroscopy (WDS), X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). The results indicate that the severe dendritic segregation exists in Al-Zn-Mg-Cu-Zr-0.12Ce alloy ingot. The as-cast microstructure mainly involvesα(Al), non-equilibrium eutectics (α(Al)+Mg(Zn, Al, Cu)2), and small amounts ofθ(Al2Cu), Al8Cu4Ce and Al7Cu2Fe phases. During homogenization, the lamellar eutectic structures in the as-cast alloy is dissolved into the matrix, meanwhile, a transformation from Mg(Zn, Al, Cu)2 to Al2CuMg phase also occurs. The overburnt temperature of the alloy is 474.87℃. The optimum parameters of single homogenization are (465℃, 40 h), which is consistent with the result of homogenization kinetic analysis. The eutectic phases are eliminated more sufficiently with two-step homogenization treatment at 435℃ for 12 h and then at 470℃ for 32 h. The residual second particles after homogenization are some small Al2CuMg, Fe-rich and Al8Cu4Ce phases.
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