Influence of Microstructure in Near‐Surface Areas of Feedstocks on the Bond Strength of Roll Bonded Aluminum Clads

Abstract

This work determines the impact of the different grain sizes and oxide layers in near‐surface areas of aluminum semi‐finished products on the bond strength after warm roll bonding. To adjust the grain microstructures in the initially twin‐roll cast feedstocks, they are differently treated to generate different grain sizes in the near‐surface areas. Semi‐finished products of the same near‐surface microstructure are then joined by warm roll‐bonding. In industrial applications, it is common to influence the bond strength of clads by applying a post heat treatment. Therefore, a part of the samples was annealed after warm roll bonding. Post‐treated samples with coarser grain size exhibit up to two times higher peel strength than untreated samples. Higher peel strengths of the post‐treated samples can be explained both by improved diffusion bonding due to heat exposure, and by recrystallization and grain coarsening of microstructure in the interface of sheets. Increase in peel strength of the composites made of feedstocks with coarser grains can be the result of stronger grain rotation, which damages oxide layer on the interface. To summarize, twin‐roll cast and soaked material with the coarsest grains in the near‐surface areas is the best feedstock for roll‐bonding, if an additional heat treatment is applied.