ON THE MECHANICAL-BEHAVIOR OF COMMERCIAL-PURITY ALUMINUM DEFORMED UNDER AXISYMMETRICAL COMPRESSION CONDITIONS

The stress-strain behavior of commercial-purity aluminum deformed unde r axisymmetric compression conditions in the temperature range of 293- 673 K is analyzed on a rational basis. The strain dependence of the fl ow stress at every temperature and strain rate is satisfactorily descr ibed by means of the exponential-saturation equation earlier proposed by Voce (1948, 1955). The temperature and strain rate dependence of bo th the initial flow stress and the saturation or steady-state stress i s analyzed in terms of two different models. First, the hyperbolic-sin e model advanced by Sellars and Tegart (1972) in terms of the Zener-Ho llomon parameter, assuming that the activation energy for deformation of this material remains constant and equal to 156 KJmol(-1) in the wh ole temperature interval. Second, the model proposed by Kocks (1976) i n terms of a power-law considering that the stress sensitivity exponen t of the strain rate is significantly temperature-dependent. This mode l leads to the introduction of a temperature-compensated strain rate p arameter similar to the MacGregor-Fisher parameter. Under the consider ation that the initial strain hardening rate should be independent of temperature and strain rate it is determined that the relaxation strai n parameter involved in the Voce equation can be calculated as a linea r function of the saturation stress. It is concluded that although bot h models describe the experimental data with similar accuracy, accordi ng to the statistical parameters calculated for every approach, Kocks model allows a somewhat better correlation with the present experiment al data. The description of the stress parameters by means of the hype rbolic-sine relationship suggests a decrease in the activation energy for deformation with temperature below 473 K. Significant deviations i n the computation of the stress-strain curves and in the description o f the work hardening behavior of the material under some deformation c onditions are still observed independently of the model employed. Howe ver, it is believed to be due to two severe requirements imposed simul taneously to the model: the description of experimental data determine d under a wide spectrum of deformation conditions while maintaining a minimum of material parameters in the constitutive functions developed . (C) 1997 Elsevier Science Ltd. All rights reserved.