Effects of Homogenization Conditions on the Microstructures of Twin-Roll Cast Foil Stock of AA8021 Aluminum Alloy

AA8021 aluminum alloy twin-roll cast strips with 7mm gauge were rolled to 3.8mm gauge sheets and given homogenization, further rolled into 0.55mm gauge foil stocks with intermediate annealing. This paper investigated the influence of homogenization conditions on microstructures of foil stocks in detail. The results show that, for the foil stock made from the sheet without homogenization, the grain structure is partially recrystallized. While the grain structure of foil stock made from the sheet with medium temperature homogenization is fully recrystallized, but it is coarse near sheet surface. However, foil stock made from the sheet with high temperature homogenization has fine and uniform recrystallized grain structures. The differences of grain structures among these three kinds of foil stocks can be understood by the variation in solid solution content of Fe, Si, Mn and distribution of intermetallic compounds. The optimized homogenization condition was adopted by our plant to produce foil stock, and its grain structure was fine and uniform. The surface quality of final aluminum foil rolled from the foil stock could meet high grade requirements of customers.

STANDARD COSMOLOGY: CAUSAL HOMOGENIZATION CONDITION AND ENERGY DISSIPATION

The effect of a transient dissipative phase, during the early evolution of the cosmic fluid, is investigated in the framework of the Extended Irreversible Thermodynamics. The role played by the bulk viscosity is considered in the case of a spatially flat Friedmann-Robertson-Walker model, and we discuss a solution which allows the condition of causal homogenization of a hypersurface t=constant to be satisfied.