The microstructure, phase composition, and microhardness of both gas-atomized and mechanically milled powders of the Al7075 + 1 wt % Zr alloy were investigated. The gas-atomized powder exhibited a cellular microstructure (grain size of a few µm) with layers of intermetallic phases along the cell boundaries. Mechanical milling (400 revolutions per minute (RPM)/8 h) resulted in a grain size reduction to the nanocrystalline range (20 to 100 nm) along with the dissolution of the intermetallic phases. Milling led to an increase in the powder's microhardness from 97 to 343 HV. Compacts prepared by spark plasma sintering (SPS) exhibited negligible porosity. The grain size of the originally gas-atomized material was retained, but the continuous layers of intermetallic phases were replaced by individual particles. Recrystallization led to a grain size increase to 365 nm in the SPS compact prepared from the originally milled powder. Small precipitates of the Al₃Zr phase were observed in the SPS compacts, and they are believed to be responsible for the retainment of the sub-microcrystalline microstructure during SPS. A more intensive precipitation in this SPS compact can be attributed to a faster diffusion due to a high density of dislocations and grain boundaries in the milled powder.

Department of Low Temperature Physics Faculty of Mathematics and Physics Charles University 5 Holešovičkách 2 Prague 18000 Czech Republic

Department of Metals and Corrosion Engineering UCT Prague Technická 5 Prague 16628 Czech Republic

Department of Physics of Materials Faculty of Mathematics and Physics Charles University Ke Karlovu 5 Prague 12116 Czech Republic

Institute of Plasma Physics of the CAS Za Slovankou 1782 3 Prague 18200 Czech Republic

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Bimodal Microstructure in an AlZrTi Alloy Prepared by Mechanical Milling and Spark Plasma Sintering

The Influence of Milling and Spark Plasma Sintering on the Microstructure and Properties of the Al7075 Alloy