The micro-injection upsetting (MIU) experiments of commercially pure aluminium have been conducted on two groups of specimens with different grain structures. One group is of coarse grain (CG, undeformed) and the other group is of fine grain (FG) achieved via the 4th pass equal channel angular pressing in micro-meso/scale. The two groups were further processed by micro/meso-scale extrusion before conducting MIU for fabricating tiny pins. Micro-upsetting test of the tiny pins showed that the material has a good isotropic flow forming and is free of undesirable defects comparing with the CG counterparts, which can be ascribed to the decreasing of grain boundary strengthening effect in the case of FG structure.
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