Mechanical modeling and microstructural observation of pure aluminum crept under constant stress

Precise constant stress creep tests were conducted on five nine pure aluminum specimen between 293 and 623 K. A well-defined steady state creep was not observed under these conditions. The macroscopic stress response of the aluminum was examined by mechanical modeling, using combinations of the Maxwell and the Voigt elements. The plastic strain changes were well described by a serial combination of the two elements using experimentally determined viscosity coefficients for both elements. These results suggested that a dual phase substructure would form in crept aluminum under constant stress and this was confirmed by direct observation, which revealed a cellular structure. The viscosity coefficient is identified with the mobility of dislocations in both phases. The temperature dependencies of both coefficients were similar with the activation energy close to that for lattice self-diffusion in pure aluminum.