Grain-size dependency on creep of pure aluminum with ultra-fine grain and coarse grain at low temperatures

To reveal grain-size dependency and mechanism of creep of 1050 aluminum at low temperatures, creep tests were performed for the samples with grain sizes (d) of 1.0-47 μ m at 233-473 K. Dislocation creep rate-controlled by non-diffusion process was observed at low temperatures, i.e., T<400 K and 280 K for coarse (CG) and ultrafine grained (UFG) specimens, respectively. The former showed creep at more than 0.2% proof stress, whereas the latter did it at less than that stress. Creep behavior of UFG aluminum was similar to ambient-temperature creep of hexagonal close-packed metals because apparent activation energy was about 30 kJ/mol. Although grain-size exponent was small, i.e. p=0-0.3, in CG and UFG regions, transient region was observed at d=1.7-10 μm and creep rate decreased of about one order. At high temperatures, CG and UFG aluminum showed conventional dislocation creep rate-controlled by dislocation-core diffusion.