Influence of homogenising temperature on the microstructure of 7085 Al alloy

The influence of homogenisation annealing process on microstrucure of 7085 Al alloy has been investigated by optical microscopy(OM), scanning electron microscopy combined with energy dispersive X-ray spectroscopy (EDX), X-ray diffraction(XRD), and differential scanning calorimetry (DSC). The results show a large amount of skeletal Mg(Zn, Al, Cu)(2) phase and AlZnMgCu phase distributed as eutectic microstructure on crystal boundaries, and some impurity phase of triangle or square Al18Mg3Cr2 in the interior of grain in as-cast 7085Al alloys. In combination with DSC and OM observation, the temperature of homogenisation annealing is determined lower than 473 degrees C. With increasing temperature of homogenising annealing, the woven crystal microstructure on the grain boundary and part lager block second phase in interior of grain decreases, and grain boundary turns to be discontinuous. 7085Al alloys are treated by homogenising annealing of 470 degrees C/24 h, grain boundary turns to be discontinuous, uniform and fine precipitation phase arises, and woven eutectic microstructure and lager block second phase disappear. The optimised homogenising annealing is 470 degrees C/24 h in the study.