Effects of Stacking Number on Microstructure and Mechanical Properties for Cold Roll Bonding Process of Dissimilar Aluminum Alloy Sheets

A cold roll-bonding (CRB) process is applied to study the effects of stacking number on the microstructure and mechanical properties of roll-bonded and age-treated Al sheets. Commercial AA1050 and AA6061 sheets with a thickness of 2 mm were stacked alternately on each other to two and four layers, and roll-bonded by multi-pass cold rolling. The roll-bonded Al sheets were then subjected to natural aging (T4) and artificial aging (T6) treatments. The as roll-bonded Al sheets showed a typical deformation structure, where the grains are elongated in the rolling direction regardless of the stacking number. However, after the T4 and T6 aging treatments, the Al sheets had a recrystallization structure consisting of coarse grains in both the AA5052 and AA6061 regions with different grain sizes in each. In addition, the sheets showed an inhomogeneous hardness distribution in the thickness direction, with higher hardness in AA6061 than in AA1050 after the T4 and T6 age treatments. The tensile strength of the T6-treated specimen was higher than that of the T4-treated one for both the 2 and 4-layer CRBs. In addition, both the tensile strength and elongation of the specimens processed by the 4-layer stack CRB were higher than those of the 2-layer stack CRB for all experimental conditions.