Evolution of Matrix Strength and Porosity During Hot Deformation of Aluminum Metals

Evolution of matrix strength and porosity during hot deformation of aluminum metals is investigated by using a multiple internal state variable constitutive theory and finite element based rolling models. The identified internal state variables in hot deformation are matrix strength and porosity, and are generally representatives of the mean, underlined microstructure states. The constitutive model is implemented in the finite element based process models to analyze hot rolling responses by which the kinetics of matrix strength and porosity are monitored. In order to develop the constitutive model, a viscoplastic potential function is evaluated with the assistance of finite element based unit cell models, in which the impact of pore shapes on the kinetics of densification is evaluated. High purity aluminum powders were used to fabricate subscale testing samples for constitutive modeling and the material was further formed into metal plates for hot rolling experiments. Uniaxial stress tests were conducted to develop the constitutive model, in which matrix strength and porosity were quantified. Plates made by the high purity material were hot rolled by a lab rolling mill where external processing parameters and internal state variables could be determined. Experimental results are compared with numerical solutions generated from the process models.