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a b s t r a c tEqual channel angular pressing (ECAP) was performed on the as-extruded commercial pure magnesium at 250 1C for 4 passes. The internal friction of the ECAPed pure Mg as a function of strain amplitude was investigated by dynamic mechanical analyzer (DMA), and the cyclic microplasticity of pure Mg was investigated by tensile loading and unloading test. After ECAP processing, the grain size is significantly refined, the texture component with basal planes parallel to extrusion direction is replaced by a new stronger one with basal planes having a tilting angle of about 401 to the extrusion direction. The stress in microplastic region is reduced with increasing ECAP passes, while the internal friction increases. The internal friction of Mg at high strain amplitude is closely related to microplastic deformation and can be interpreted by dislocation mechanism. The Granato and Lücke model only satisfies in anelastic regions, while the internal friction in microplastic deformation region should be explained in terms of the internal friction model postulated by Peguin. The internal friction related to microplasticity can be divided into two parts with different activation volumes of dislocation motion, which correspond to the two regions of microplasctic deformation process. The initial stage associated with dislocation motion on basal plane shows larger activation volume and lower friction stress of dislocations. The second stage related to the annihilation and tangle of dislocations is characterized by larger hardening exponent and friction stress.

In-situ synchrotron diffraction and atom probe tomography (APT) have been used to study the carbon diffusion and redistribution process in austempered ductile iron (ADI) during austempering. The process of carbon content change in bainitic ferrite during different austempering temperatures has been determined quantitatively. The transformation in ADI is controlled by decarburization of supersaturated ferrite and carbide precipitation and has been found to be divided into three stages based on a model developed for bainitic steels by Takahashi and Bhadeshia. The formation, morphology and composition of carbides and carbon clusters in ferrite after austempering have been identified unequivocally by APT. Finally, the relationships of carbon content in ferrite, carbon gap values, and austempering temperatures in the ADI alloy were expressed using empirical equations.