The influence of deformation conditions in solid-state aluminium welding processes on the resulting weld strength

Solid bonding of aluminium is an important joining technology with applications in fabrication, forming and new low-carbon recycling routes. The influence of deformation conditions on the strength of the resulting weld has yet to be fully assessed, preventing optimization of current processes and development of new ones. In this work, an extensive literature review identifies the deformation parameters important to weld strength: interface strain, strain rate, normal contact stress, temperature and shear. The film theory of bonding is used to derive a model that quantifies the relevance of these parameters to the weld strength. This model is then evaluated using an experiment in which the interface strain and normal contact stress are decoupled, and the friction hills between both the tooling and the samples and between the samples themselves minimized. Neither the model nor the experiments deal with samples that have undergone mechanical surface preparation (for example, scratch brushing) prior to bonding. The experiments show that a minimum strain is required for bonding. Increasing the temperature, normal contact stress or shear stress can reduce this minimum strain. A normal contact stress above the materials' uniaxial yield stress is necessary to produce a strong bond. Increasing the strain rate has little affect on the weld strength for bonds created at low temperatures, but can significantly reduce the strength of bonds created at higher temperatures. The proposed model correctly predicts these trends; however, for higher temperatures it underestimates bond strengths and the influence of strain rate, suggesting that diffusion mechanisms increase the strength of bonds created at higher temperatures. (C) 2014 The Authors. Published by Elsevier B.V.