Abstract
Atomized powder of an Al7075 alloy was high energy ball milled at room and cryogenic temperatures and compacted by spark plasma sintering (SPS) method. The influence of processing parameters on phase composition and microstructure was studied by X-ray diffraction, light and scanning electron microscopy.
The mechanical properties were characterized by microhardness measurements. The atomized powder contained a large volume fraction of intermetallic phases located predominantly in continuous layers separating cells or dendrites in the interior of individual powder particles.
Consolidation by SPS destroyed partially this morphology and replaced it by individual particles located at boundaries of original powder particles, at cell boundaries or arranged in chains in previous dendritic regions. High energy milling destroyed most intermetallic particles and enriched the matrix by solute atoms.
The high deformation energy introduced into the powder during milling enhanced microhardness up to 220 HV. Consolidation of milled powders by SPS led to the formation of very fine-grained structure with the grain size even below 1 mu m and with the fraction of high-angle boundaries about 0.9.
Two main types of heterogeneously distributed precipitates were found. The irregularly shaped precipitates with a size about 1 mu m seemed to encompass areas with rod like nano-precipitates in most samples.
A drop in microhardness to 118HV was observed after SPS, predominantly due to a release of introduced deformation energy.