| At present,CZ-9 is in the pre-research stage and is expected to be launched in 2028.The diameter of the rocket fuel tank is 9.5 m,the thickness is 18 mm,and the material is 2219 aluminum alloy.2219 aluminum alloy has the advantages of excellent high-temperature mechanical properties,high fracture toughness and good stress corrosion resistance.It has become the first selected for heavy-lift launch rocket fuel tank materials.Friction stir welding(FSW)is a solid-phase welding method,which is widely used in the welding of 2219 aluminum alloys due to its small grain size,good connection strength and tensile strength,and small residual stress after welding.However,when FSW 2219 aluminum alloy thick plate,the phenomenon of uneven heat input along the thickness of the weldment will appear,which further affects the mechanical properties of the welded joints,and it is difficult to obtain a tensile strength equivalent to that of thin plate welding.At present,the FSW temperature distribution law of 2219 aluminum alloy thick plate is unknown,and the core area temperature is difficult to characterize due to the shielding of the shoulder,the complex heat generation and heat transfer mechanism.How to reasonably select the welding process parameters to ensure the welding quality is still in the exploratory stage.In view of the above problems,this paper studies the FSW temperature field simulation of 2219 aluminum alloy thick plate,the temperature characterization in the core area of weldment and the optimization of welding process parameters.The specific research contents are as follows:Combining heat transfer theory,rigid visco-plastic theory and simulation technology,a FSW 2219 aluminum alloy thick plate temperature field simulation model based on DEFORM is established,which realizes the simulation of the plunging,dwelling,welding and tool withdrawal phases.The support vector regression machine is applied to the research on the temperature characterization in the core area of weldment,and the optimization of the penalty coefficient and kernel parameter is realized using MATLAB.Taking temperature data of the feature points on the surface of weldment as input,the maximum and minimum temperature prediction model in the core area of weldment are established,and the maximum and minimum temperature prediction in the core area of weldment is realized.Taking 80% of the solidus and liquidus temperature of the aluminum alloy as the reasonable welding temperature range,and taking the minimum temperature difference in the core area of weldment as the optimization goal,an orthogonal test is designed to study the effect of the welding process parameters on the temperature difference during the plunging and dwelling phase,the primary and secondary order of the influence of welding process parameters on the temperature difference in the core area of weldment is explored.A two-factor experiment is designed to study the influence of the rotational speed and the dwelling time on the maximum temperature,the minimum temperature,the temperature difference and the reduction rate of the temperature difference in the core area of weldment,the optimization of welding process parameters during the plunging and dwelling phase is realized.A two-factor experiment is designed to study the influence of the rotational speed and the welding speed on the maximum temperature,the minimum temperature and the temperature difference in the core area of weldment during the welding phase.The welding process parameter combination that meets the requirements of the optimum welding temperature is obtained by surface fitting,and the experimental verification is carried out.The research in this paper provides theoretical and technical references for revealing the FSW temperature distribution law of 2219 aluminum alloy thick plate,optimizing welding process parameters and ensuring welding quality,and providing support for the realization of high-quality welding of heavy-lift launch rocket fuel tanks. |
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