Microstructural Evolution of Roll Bonded Al-Clad Stainless Steel Sheets at Elevated Temperatures

The cold roll bonding of Al on AISI 304L stainless steel was carried out to fabricate the Al 304L/Al clad sheet composites. The maximum bond strength of 20 N/mm was acquired just by 38% reduction, for which the tearing of the aluminum sheet occurred during the peeling test. The microstructural evolution during subsequent postannealing heat treatment was systematically studied based on the impurity diffusion coefficients, microhardness measurements, X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM) images and energy dispersive X-ray analysis (EDS) spectra to pave the way for successful applications of these composite sheets. An intermediate layer composed of intermetallics of Al and Fe was found to form on the aluminum side of the roll bonded sheets, showing that this layer was formed by the diffusion of elements from the 304L sheet to the aluminum sheet due to the faster diffusion of Fe in Al. Moreover, the calculated diffusion distances were in a good agreement with the results obtained from the line scan EDS analysis and the microhardness profile. It was also found that the presence of the strain-induced martensite in the 304L sheet did not exert any effect on the intermediate layer.