Microstructure of spray formed Al-Zn-Mg-Cu alloy with Mn addition

With the aim to improve the strength of Al-Zn-Mg-Cu alloy, the alloy billet containing Mn was produced by spray forming method, and the microstructural features were investigated using X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The results show that the billet mainly consists of fine equiaxial grains of MgZn2 and Al6Mn with size ranging from 5 μm to 25 μm. Nano-scaled MgZn2 is dispersed in the as-sprayed alloy, primary Al6Mn particles are precipitated at grain boundaries with an average size of 5 μm. A few CuAl2, Al3Zr and eutectic are also found in as-sprayed Al alloy. The volume fraction of the porosity is about 12%. DSC result indicates that most of the solutes are precipitated during spray forming process, and no obviously thermal effects occur below 450 °C. Both matrix grains and Al6Mn particles grow monotonously with the increase of annealing temperature, but the growth rate of Al6Mn particles is markedly lower than that of Al grains, and the matrix grains grow rapidly when the annealing temperature is above 375 °C.