HOT DEFORMATION MECHANISMS IN COMMERCIAL PURITY ALUMINUM

The hot deformation processes taking place in commercial purity alumin ium with 0.22% Fe and 0.14% Si content are investigated by tensile tes t, impression creep, and direct extrusion experiments. The stress-srai n rate relationship obtained at different temperatures can be describe d by a power function. In the low and medium stress regions correspond ing to strain rates between 10(-6) and 100 s(-1) and to temperatures h igher than 300 to 350 degrees C the deformation process can be charact erized with a constant activation energy of about 200 kJ/mol and with a stress exponent of about n = 7 independently of the mode of deformat ion. These relatively high values may be connected with the large numb er of intermetallic particles inherited from the cast state. At higher stresses attained by lowering the temperature below 350 degrees C the stress exponent is increased up to n = 12 to 13, and the activation e nergy is decreased to that of grain boundary diffusion. The latter pro cess is also found to be similar in the case of creep and hot extrusio n processes.