Casting aluminum alloys are highly heterogeneous materials with different types of voids that affect the mechanical properties of the material. Through the analysis of a cylindrical void-cell model the evolution equation of the voids was obtained. The evolution equation was embedded into a nonclassical elastoplastic constitutive relation, and an elastoplastic constitutive relation involving void evolution was obtained. A corresponding finite element procedure was developed and applied to the analyses of the distributions of the axial stress and porosity of notched cylindrical specimens of casting aluminum alloy A101. The computed results show good agreement with experimental data.
The dynamic softening behaviors during hot deformation of 7075 aluminum alloy were studied by isothermal hot compression tested at temperatures of 250, 300, 350, 400 and 450 ℃ and strain rates of 0.01, 0.1, 1 and 10 s-1 on Gleeble1500. The results show that the temperature changes have a significant effect on the dynamic softening rate. It is indicated that the considerable dynamic softening rate associated with dynamic recrystallization leads flow stress value decreasing gradually. A group of coefficients needed by the phenomenological constitutive model containing a softening ratio item were calculated by the multiple linear regression method. The optical microstructures show that the grains of billets compressed become more and more refined with strain rate increasing as well as the degree of dynamic softening and work-hardening higher. The phenomenological constitutive description of 7075 aluminum alloy can accurately describe the relationships among flow stress, temperature, strain rate, strain and dynamic softening, and offer the basic model for plastic forming process simulation.
