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Microstructure and properties of ball milled and hot compacted powder of 7055 aluminium alloy

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7xxx series (Al-Zn-Mg-Cu) aluminum alloys are widely used in the aircraft industry due to their low density, high strength and good workability [1, 2]. Their strengthening increases with the concentration of Zn and is associated with higher density of very fine precipitates of metastable η′-phase enriched with Zn and Mg. The high solute (about 8 wt. % of Zn) alloy designated AA 7055 (ALCOA) evokes the highest strength aluminium alloys produced by ingot metallurgy and is applied as upper wing skin materials in commercial aircraft [3]. The 7055 composition processed using the T77 temper provides a microstructure at and near grain boundaries that is resistant to both intergranular fracture and interglanular corrosion. Aluminium based materials produced by powder metallurgy (PM) processing offer a number of interesting opportunities for high strength applications. Powder metallurgy enables to fabricate high quality parts close to final dimensions with refined microstructure as compared with these produced by the conventional ingot metallurgy [4, 5]. The ball milling applied before the compaction allows obtaining a very fine microstructure and the extension of the solid solubility limits of the elements added to the alloy [6]. It results in improved mechanical and corrosion properties of the compacted products. PM technology provides more homogenous distribution of the precipitates and reduces the particle size that makes corrosion more uniform [7]. The aim of the present investigation was to study the effect of ball milling and hot pressing on the microstructure and properties of milled and compacted 7055 aluminium alloy powder. Exp erimental details The mixtures of elemental powders of aluminum, zinc, magnesium, copper and zirconium were used as starting materials to yield (wt. %) Al - 8% Zn - 2% - Mg - 2.3% Cu - 0.2% Zr compositions corresponding to 7055 commercial aluminium alloy. The ball milling of the powder was [...]

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