EFFECT OF THE COMPACTION PARAMETERS AND CANNINGMATERIAL OF NANOSTRUCTURED AL-POWDER CONSOLIDATED VIA INTENSE PLASTIC STRAINING PROCESS

摘要

Research groups around the world have reached common and contradicting conclusions regarding the behavior and properties of nanostructured materials. The aim of this research is to affirm the common findings by previous research, and support one of the currently proposed concepts of mechanical behavior based on processing and characterization of consolidated nanocrystalline micropowders of high strength/precipitation hardenable aluminum alloy using combined PM/intense plastic straining via Equal Channel angular Extrusion (ECAE). This research work investigated the effect of (a) Cold and hot consolidation of nanocrystalline Al-2124 micropowders into compacts with 4.0 h/d ratio and (b) Canning material used for encapsulating the compact rods for subsequent extrusion within the ECAE channels, and (c) the effect of ECAE number of passes and routes on the green compact properties. The effect of the processing parameters (compaction condition, extrusion temperature, strain rate) on the sample density, grain, subgrain and subcell sizes, and hardness was studied. Pure wrought and cast Cu, and casts Al-cans as well as Al-2024 wrought cans were used for canning of the consolidated powders. Green and hot compact rods were produced from 40μm average particle size Al-2124 powders with 53nm internal structure. Highest density consolidated rods were produced for the double sided cold compaction at 60 (450MPa) over duration of 30min, while single sided compaction at similar pressure over 60min duration time of compaction and at temperature of 480℃ produced the most dense and highest hardness hot compacts. Pure wrought Cu and cast Al are the most suitable canning material for room temperature ECAE of the Al-2124 green compacts. Non-isothermal heating during extrusion hindered the uniform warm deformation of the green and hot compacts canned in wrought Al-2024. Loose powder particles of the green compacts results in particle rotation while passing though the 90° angle intersecting channels of ECAE, and hence prevents full consolidation and densification of the produced product.