Layer continuity in accumulative roll bonding of dissimilar material combinations

Strips were made by accumulative roll bonding of up to 64 alternating layers of an AA3103 alloy and either commercial purity copper or CuZn20 brass as the second type of layer. With increasing number of accumulative roll bonding cycles the layered structure became unstable. Instability in the strongest layer observed by secondary electron micrographs and orientation imaging micrographs revealed shear bands through the strong layers. The influence of the layer instability on the mechanical properties was investigated by tensile tests and three point bending tests. Numerical simulations using the commercial finite element software DEFORM 2D were used for investigating the instability mechanism in deformation of the multilayers. It is argued that the earlier proposed explanations and analytical estimates of the necking in the hard layers due to internal stresses do not apply. Instead the onset of the instability is in the form of a zigzag-shear instability, where the layers experience periodic increased thinning and bending.