An analytical simulation of solidification behavior within deposited preform during spray forming process

Solidification within spray deposited preform is one of the key processing stages of spray forming, which has a substantial influence on the formation of the final microstructure of the preform. For the sake of optimizing the process and getting desired microstructure and properties of the preform, the solidification behavior should be fully understood. In this investigation, a concept of 'virtual' solidification layer was applied to establish an analytical model to simulate the solidification behavior within the preform during spray forming process, which will provide clearer physical pictures of the solidification behavior. According to the model developed, a simulation of the solidification behavior was performed for a typical Al-Cu alloy. The results show that both the processing parameters (such as deposition rate and temperature of spray cone at the point of impingement) and the thermophysical properties of the material are the important factors controlling the solidification behavior. Even for the same thermodynamic state of spray cone at the point of impingement, the top surface temperature of the preform will change conspicuously as variation of the processing parameters or thermophysical properties of the material takes place, which will cause the variation of microstructure and properties of the preform. Therefore, the principle of taking the thermodynamic state of spray cone at the point of impingement as the key factor controlling the spray deposition process should be modified adequately. A new parameter (the surface temperature of the preform) for the processing control of spray forming was proposed. (C) 2000 Elsevier Science S.A. All rights reserved.