| The milling deformation and controlling of the large aviation overall structure are the current hotspot and difficult issues. Generally the large-scale billet material is obtained by joining, so the joining processes and the status of connection zone will affect the subsequent milling deformation seriously. In this paper, the billet material is joined by friction stir joining (FSJ) technology and the high-strength aluminum alloy 7022 is selected as the study object, then the influences of the joining processes on the integrity of the connection area were studied systematically. On the basis of this, the sequent milling deformation of joining billet material was predicted, which provide the foundation for controlling the processing deformation of the large-scale aviation structure. The main work and the achievements accomplished in this article are listed as following:1. The metal plastic flow processes of connecting zone for the aerospace aluminum alloy 7022 joined by friction stir joining were analyzed. The cross-section of the connecting area is analyzed by metalloscope and tool-microscope method, then the plastic flowing law of connecting area is obtained. The theoretical analysis shows the correctness of the metal plastic flowing law and the corresponding model is established.2. The rules of the major process parameters on the mechanical properties of connecting zone are studied, and the mathematical model of the force on the stirring head is established. Combined with the theoretical and experimental results, the FSJ operating parameters of 10mm thick 7022 aluminum alloy is determined. And the process parameters are further optimized to obtain better results of the connecting zone by analysis on the mechanical properties. At the same time, the force testing of the pin is carried out for the subsequent FSJ simulation. Then the mechanical model of FSJ is established by the orthogonal experimental method.3. Research on the simulation and experimental result of FSJ temperature field. The heat source model in FSJ process is established. Firstly the temperature field of FSJ is simulated by the ANSYS software, then the contour of temperature field and the temperature variation trend in the welding process are obtained. In addition, the temperature cycling curves under different operating parameters are analyzed, which prove the validity of our model.4. Research on the FSJ residual stress and deformation principles. The thermal-mechanical coupling model of FSJ is simulated by the ANSYS software, then the distribution of the FSJ residual stress and the deformation curves are obtained. Comparing the simulation results with the experimental results, we found they coincided with each other very well. On this basis, the FSJ residual stress distribution and deformation principles of the large-size case are further predicted.5. Research on the residual stress distribution and the milling deformation of joining billet material. Considered the effect of residual stress distribution within the billet joining material to the subsequent milling deformation, corresponding numerical simulations were carried out and the milling deformation curve of joining billet material was obtained. The validity of this model is proved by our experiment. Beyond this, the milling deformation trend of the large size joining billet material was analyzed and the deformation law of milling of the large size joining billet material was predicted. In the last, a new prediction and analysis software for milling deformation of aviation aluminum alloy joining billet material was developed.
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