Light-weight materials produced by accumulative roll bonding

Abstract

The work presented in this thesis is an experimental study of roll bonding and accumulative roll bonding of similar and dissimilar metal combinations with special focus on bond strength evaluation, post process heat treatments and layer continuity of the harder phase. Three objectives have been pursued. The first objective was development of a new method to test the bond strength in tensile mode. The second objective was to assess the influence of post deformation heat treatments on the mechanical properties of the material. Hardening on annealing has been mainly investigated in cold rolled and accumulative roll bonded AA3103 aluminium alloy. The third objective was to analyze instabilities and the continuity of the hard layer in accumulative roll bonding of dissimilar material combinations.

The thesis is organized into two parts. The first part is a synopsis that includes the theoretical background and literature review, scope and objectives, a brief description of the various experimental techniques used in the work and concluding remarks. Some recommendations have also been made for future work. The second part of the thesis consists of three articles published or submitted for publication to scientific journals. These articles provide a detailed description of the results of the various experiments carried out with supporting discussion and conclusions.

The first article presents a new method developed for testing the bond strength of roll bonded aluminium sheets in the tensile mode across the interface. Two different aluminium alloys AA3103 & AA1200 in two different temper conditions - ‘O’ and ‘H19’ were subjected to roll bonding with progressively increasing thickness reductions and the tensile bond strength was measured by ripping apart the bonded interface using an adhesive. The influence of the temper conditions and strength of the starting material on the bond strength has been discussed in addition to the effect of increasing deformation.

The second article deals with the hardening on annealing behavior observed in cold rolled and accumulative roll bonded AA3103 alloy. The hardening on annealing behavior is investigated over a broad range of temperatures and annealing times by tensile tests and the effect of strain on the behavior is documented. The contribution of different mechanisms to this behavior is discussed and analyzed. Alloying elements like Si & Mn have been finally reported to contribute significantly to the hardening on annealing in AA3103 alloys by formation of clusters.

The third article presents an investigation on instability and continuity of the hard layer in accumulative roll bonding of dissimilar material combinations. The two dissimilar combinations investigated were AA3103/CuZn20 Brass and AA3103/commercial pure Copper. Tensile tests and three point bend tests are used to investigate the influence of instabilities on the mechanical properties. Numerical simulations of plane strain compression and multi-layer roll bonding using the commercial package DEFORM 2D have been used to observe and analyze the instability mechanism. Applicability of the earlier proposed explanations and mechanisms for necking in the hard layer is discussed and a form of zig-zag instability is suggested to cause the onset of instabilities in the hard layer.