Construction of Consolidation Maps of Pre-ECAE Hot Compact Nanocrystalline-Micron Powders

摘要

The Equal Channel Angular Extrusion (ECAE) process is one of the most promising processes used for producing nanostructured consolidates making use of the severe plastic conditions that the powder particles experience during the extrusion. The intrinsic heat generated during extrusion in addition to 1.16 total strain imposed on the powder per pass can substitute for the elevated temperature required for sintering. The consolidation conditions of the Nanocrystalline-Micropowder (NCMP) prior to ECAE influences significantly the structural evolution and hence mechanical properties of the produced bulk product. Through the current research work, consolidation maps of hardness and density variation for NCMP Al-2124 powders hot compacts were constructed. A NCMP of about 45 μm particle size and 87nm internal structure average size was used. Hot compacts of height-to-diameter (h/d) ratio of 4 were obtained by combinations of temperatures (360, 420 and 480℃), durations (30, 60, and 90 minutes), and pressures (4, 5, and 6) multiples of the yield strength (σ_(ys)) of as received Al-2124. For the NCMP hot compacts, an optimal combination of compaction conditions was for 60min duration at 420-to-480℃ range of temperatures, and 375-450MPa (5-6σ_(ys)) range of pressure. For the 30 and 90min compaction durations the optimum properties were limited to 480℃ over a stress range of 5.2 to 5.8σ_(ys). Uniformity of density along the sample's length was achieved for NCMP hot compacts at the conditions of (6σ_(ys) (450MPa), 420℃-480℃ and 60 minutes), and (5σ_(ys) (375MPa), 420-480℃ and 90 minutes). Fully dense uniformly deformed bulk products with enhance hardness up to 178% compared to the hot compact was achieved post one-pass and 2-pass routes A and C at extrusion temperature of 235℃.