Effects of temperature, strain rate and specimen size on the deformation behaviors at micro/meso-scale in ultrafine-grained pure Al

An ultrafine-grained (UFG) high purity (99.999%) aluminum with the average grain size of ~ 1.0 μm was processed using equal-channel angular pressing (ECAP) through 8 passes. The UFG pure Al was annealed at different temperatures to obtain different grain sizes. Micro-compression testing was conducted with the specimen diameters of 2.0, 1.0, and 0.5 mm at elevated temperature and with the strain rate ranging from 3.3 × 10^{− 4} to 0.1 s^{− 1}. The results show that UFG pure Al has a strong temperature dependence and high strain rate sensitivity (SRS) compared with the coarse-grained (CG) pure Al. It is found the flow stress decreases with specimen size during micro-compression of both CG and UFG pure Al, which demonstrates that UFG pure Al still exhibits the conventional size effect of micro-forming. However, the significant improved surface roughening effect in micro-compression of the UFG pure Al demonstrates that UFG materials have a potential application in micro-forming to fabricate MEMS components.