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Micro-compression testing was conducted using high purity Al processed by equal-channel angular pressing (ECAP) with both coarse-grained (CG) and ultrafine-grained (UFG) samples. The effects on the flow stresses of the initial grain size and the specimen size were investigated and the results show the initial grain sizes and the specimen dimensions affect the flow stresses during micro-compression for both CG and UFG specimens. There is a transition from strain hardening to strain softening with decreasing grain size during micro-compression but the transition grain size is dependent upon the size of the specimen. These results are interpreted using a model based on the separate influences of dislocation annihilation and dislocation accumulation in the UFG and CG materials, respectively. The results demonstrate that the occurrence of surface roughening is improved when using UFG pure Al and this shows there is a significant potential for using UFG pure Al in micro-forming operations.

A very high-purity (99.999%) aluminum was processed by equal-channel angular pressing (ECAP) at room temperature through 1 to 8 passes using a die with a channel angle of 90°. Analysis shows that processing by ECAP produces an ultrafine-grained (UFG) structure with a grain size of %1.3 mm and with microhardness and microstructural homogeneity. The mechanical properties and the fracture behavior were evaluated using micro-tensile testing after ECAP processing. A micro-forming process was used to fabricate a micro-turbine at ambient temperature and subsequent examination demonstrated that UFG pure aluminum gives higher strength and more uniform mechanical properties by comparison with conventional coarse-grained pure aluminum. The results confirm the very significant potential for using UFG pure aluminum for micro-forming at ambient temperature.

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Micro-forming with ultrafine-grained (UFG) materials is a promising direction for the fabrication of micro-electro-mechanical systems (MEMS) components due to the improved formability, good surface quality, and excellent mechanical properties it provides. In this paper, micro-compression tests were performed using UFG pure aluminum processed by equal-channel angular pressing (ECAP) with subsequent annealing treatment. Microstructural evolution was investigated by electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). The results show that microstructural evolutions during compression tests at the micro/meso-scale in UFG pure Al are absolutely different from the coarse-grained (CG) materials. A lot of low-angle grain boundaries (LAGBs) and recrystallized fine grains are formed inside of the original large grains in CG pure aluminum after micro-compression. By contrast, ultrafine grains are kept with few sub-grain boundaries inside the grains in UFG pure aluminum, which are similar to the original microstructure before micro-compression. The surface roughness and coordinated deformation ability can be significantly improved with UFG pure aluminum, which demonstrates that the UFG materials have a strong potential application in micro/meso-forming.

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