Evolution of eutectic structures in Al-Zn-Mg-Cu alloys during heat treatment

The evolution of the eutectic structures in the alloys with different copper contents during heat treatment was studied by scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy(EDS), and differential scanning calorimetry(DSC). The as cast microstructures involve alpha(Al), eutectic(alpha(Al) + Mg(Al, Cu, Zn)(2)) and Al7Cu2Fe. The Al2CuMg particles form during heat treatment. The volume of coarse phases decreases quickly in the initial 12 h during heat treatment. The volume of coarse phases change a little at 400 and 420 degrees C. Copper content has a great influence on the evolution of the eutectic. The coarse phases dissolve slowly in alloy with higher copper content.