Abstract
A re-evaluation has been made of the mechanism of bonding in cold pressure welding by rolling. In the experimental work, composites of commercially pure aluminium have been rolled to deformations of up to 75% and two testing methods have been used to measure the ultimate shear strength of the formed welds. Metallographk observation has shown that below the threshold deformation the unwelded surfaces consist of the original scratch-brushed areas and regions of the underlying base metal which are revealed but cannot weld, owing to the presence of contaminants. A major feature of the bonding mechanism described in this paper is that such contaminated areas remain unwelded even at the higher rolling deformations so that the final weld strength is a function of(lie metallic area revealed after the threshold deformation. The area welded has been calculated from this proposition and the results compare well with the proportion of welded area measured from micrographs of the fracture surfaces. A general equation for weld strength v. rolling deformation has also been developed from the proposed model. The curves from this theoretical expression show good agreement with the experimental data from the present work on aluminium and previous work on other materials.
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