Hot compression bonding of AA6061: A computational study of interface conditions and their relation to bond strength
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Multi-layered engineering structural components are highly attractive in the automobile and aerospace industries. Such composite components are comprised of several metallic layers joined together to make one sheet, tube or rod [1,2]. Since each layer can have very different physical, thermal, and mechanical properties, it is theoretically possible to tailor the effective properties of the composite component to the required engineering application [2]. From a mechanical viewpoint, the strength of the interface between the different layers is a critical parameter for any load bearing application. Currently the exact relationship between the conditions at the bonded interface during the bonding process and the resulting bond strength is still an open question. In the current study, joining of AA6061 specimens using hot compression bonding is investigated. Hot compression tests of bar specimen pairs at 300-500oC and under different strains and strain rates were conducted. Following the compression tests, tensile testing was performed in order to break the bonded joints and quantify the interface bond strength. A coupled thermo-mechanical finite element model of the bonding stage was developed in order to better understand the thermo-mechanical fields that develop at the specimen interface. The computations show that the time dependent thermal and mechanical fields are inhomogeneous across the bonding interface. Microscopic characterization of the debonded surfaces show an interesting correlation between the computed principal plastic strain fields at the interface and the areas that underwent diffusion bonding. Following these findings and using the computed fields, a scalar parameter J (based on [3]) which depends on the local strain and temperature history is introduced. The relation between the value of J and the bond strength under different bonding conditions is shown.
