Fabrication of high performance PM nanocrystalline bulk AA2124

Abstract

AA2124 nanopowders <100 nm in particle size and 20 nm internal structure produced by high energy ball milling of gas-atomized micronpowders ̃45 lm in particle size and 700 nm internal structure were processed in to bulk rods. The micro- and nanopowders were hot compacted using uniaxial pressing for preliminary densification at 0.7T m of the alloy. Selected intact hot compacts (HCs) were promoted for warm severe plastic deformation via equal channel angular pressing (ECAP) at the minimum possible deforming temperature for final densification. Effect of the fabrication method of the consolidated powders was investigated. A combined processing via HC/ECAP produced bulk nanostructured rods 2.5 μm and 50-60 nm in grain size for the micro- and nanopowder consolidates, respectively. The powder properties controlled the degree of densification and mechanical behavior during the hot compaction stage, which influenced strongly the deformation behavior during subsequent ECAP. At the end of HC/ECAP one pass, the HC stage was responsible for about 83 and 95% of the total grain coarsening encountered for the microand nanopowder HCs, respectively. Throughout the various consolidation stages employed, the ball-milled (BM) nanopowder consolidates exhibited 2/3 the grain growth and displayed almost twice the hardness and compressive strength values of the gas-atomized micronpowder ones. Influence of BM and HC on the Al 2O 3 layer formed around the individual powder particles was also investigated. © ASM International.