Al-7.8Zn-1.6Mg-1.8Cu合金铸锭及其均匀化的微结构研究

Investigation of microstructures in as-cast and homogenized Al-7.8Zn-1.6Mg-1.8Cu aluminum alloy

采用光学金相(OM)、扫描电镜(SEM)、透射电镜(TEM)、X线衍射(XRD)、差示扫描量热(DSC)等技术研究Al-7.8Zn-1.6Mg-1.8Cu(7085型)合金铸锭及其均匀化的微结构。研究结果表明:该铝合金铸锭中主要结晶相为分布在晶界的网状Mg(Zn,Al,Cu)2相,晶内有少量微米量级球状和纳米量级条状的Al2Cu结晶相,此外,还有纳米量级Al2Cu和Fe-rich析出相;在均匀化过程中,Al3Zr粒子析出,Mg(Zn,Al,Cu)2相溶解消失,且部分转化成Al2CuMg相;当均匀化温度升高到470℃时,除Fe-rich相和Al3Zr粒子外,其他第二相都溶入基体;于400℃/12h+470℃/12h双级均匀化比于470℃/12h单级均匀化更有利于提高Al3Zr粒子析出的数量和改善其分布均匀性。

Microstructures in the as-cast and homogenized Al-7.8Zn-1.6Mg-1.8Cu aluminum alloy （7085 type） were investigated using optical microscopy （OM）, scanning electron microscopy （SEM）, transmission electron microscope （TEM）, X-ray diffraction（XRD） and differential scanning calorimetry （DSC）. The results show that the second solidifying phases in the ingot include a large mount of skeletal Mg（Zn, Al, Cu）2 phase, which are distributed on boundaries, and there are a little of micrometer-scale spherical and nanometer-scale club-shaped Al2Cu particles within grain. Precipitating Al2Cu and Fe-rich particles are in the ingot. During homogenization, Al3Zr particle precipitates, dissolution and transformation into Al2CuMg of the Mg（Zn, Al, Cu）2 phase occur in the mean time. Except Al3Zr and Fe-rich particles, other second phases dissolve into the matrix completely while homogenized at 470 ℃. The number density of the Al3Zr precipitation particles is larger, and the distribution of the Al3Zr precipitation particles is more homogeneous comparing the two-stage homogenization of 400 ℃/12 h ＋ 470 ℃/12 h with that of 470 ℃/12 h.