Study On Model Of Interfacial Void Evolution In The Press Bonding

Press bonding is an advanced joining method, in which a joint having microstructure and properties distinguishable from those of base material will be formed between two faying surfaces at elevated temperature using an applied pressure for several time. Press bonding technology is urgently to be developed by aerospace, aviation, automobile, energy and other fields since it provides a feasible way to manufacture multipoint, hollow structural and large area bonding components. The extent of void closure in the bonding interface affects the quality of press bonded joints, so the elimination of interfacial voids from the bonding interface is the most important step to improve the quality of press bonded joints. However, the selection of bonding parameters in the engineering application usually depends on the experiments and experiences, it will waste a lot of manpower and material resources, but also bring big error. Thus, effective prediction of the extent of void closure at a given bonding parameters becomes very important. To this end,the model of interfacial void evolution is established to predict the process of void evolution for press bonding in this study. A brief introduction to the work and its main achievements obtained are as follows.Based on local plastic flow mechanism, viscoplastic flow mechanism, surface source diffusion mechanism and interface source diffusion mechanism,a three-dimensional void evolution theoretical model is established to predict the process of void evolution. The void evolution in the present model is pictured as a two-stage process: in the first stage surface asperities as a result of prior surface treatment are flattened and the isolated voids form in the bonding interface by local plastic flow mechanism, and in the second stage voids are reduced in size by combined effects of viscoplastic flow mechanism, surface source diffusion mechanism and interface source diffusion mechanism.The dynamic conditions for those mechanisms acting on the void evolution are determined, and the effect of each mechanism on void evolution is considered based on the dynamic condition of each mechanism. In addition, the effect of macroscopic deformation of joined specimen resulted from viscoplastic flow mechanism is condiered, and the effect of stress states on void evolution is also analyzed. The results show that the void volume gradually decreases when the pressure is applied on the joined speciemen, but the varation of void radius and height depends on the ratio of applied stress between radius direction and height direction. Finally, a number of press bonding experiments of TC4 alloy have been conducted to verify the model, and the experimental results of area fraction bonded are in a good agreement with thecalculated ones via model, indicating that the three-dimensional model can give an accurate description of void evolution in press bonding.