Microstructural evolution during the initial stages of spray atomization and deposition

The material used in the present investigation was 7150 Al with a composition (in wt%) of 5.9--6.9 Zn, 1.9--2.5 Cu, 2.0--2.7 Mg, 0.12 Si, 0.15 Fe, 0.10 Mn, 0.08--0.15 Zr, 0.04 Cr and 0.06 Ti, balance aluminum. The spray atomization and deposition experiment was conducted as follows. The alloy was melted and superheated to 850 C. The molten material was disintegrated into a dispersion of micron-sized droplets by using nitrogen at a pressure of 1.20 MPa. Subsequently, the atomized droplets were deposited onto a water-cooled copper substrate to be collected as a coherent, dense preform. The substrate was positioned at a distance of approximately 36 cm below the atomizer. The microstructural observation of the as-deposited material was conducted by using optical microscopy. Samples were sectioned along the central line of the deposited material. The polished samples were etched by using Keller`s reagent. The grain size was measured through the line intercept method.