Analytical modelling of solidification during temperature gradient TLP diffusion bonding

Imposing a temperature gradient when transient liquid phase (TLP) diffusion bonding is the basis of a new bonding method which has recently been developed in the Department of Materials Science and Metallurgy, University of Cambridge (UK Patent 9709167.2). The use of temperature gradient TLP diffusion bonding results in joints with excellent reliability and also shear strengths as high as those of the parent material (e.g. aluminum-based alloys and composites). Another feature of this new method is that diffusion of solute in the solid phase is not necessary for solidification to take place and therefore bonding times are significantly shorter than those in conventional TLP diffusion bonding (when there is no imposed temperature gradient across the liquid phase). A mathematical model is proposed in this paper which is capable of predicting bonding times and bond line displacements when TLP diffusion bonding under a temperature gradient. The bond line displacement and bonding time predicted by the model for an ideal Al-Cu binary system are compared with experimental results obtained using pure aluminum and copper. The theoretical values predicted by the model are in agreement with the experimental results.