Resistance Heating Forming Processes And Equipments Of 5A90 Al-Li Alloy Stringers

Lightweight is one of the main ways to achieve the target of energy saving in automotive, aerospace and any other industrial fields, and the key method to achieve lightweight is utilizing light alloys with high performance. Al-Li alloy is a new type of light metal material, which shows strong competitiveness and broad prospects in aerospace field because of its low density, high specific strength and stiffness combined with excellent low temperature performance, corrosion resistance and superplastic formability etc. However, to some extent, its poor room-temperature formability thwarts further use and popularization, and the disadvantages of troditional hot forming methods such as high energy consumption, low efficiency, complex equipments and short life of dies does not accord with the contemporary conception and theme of advanced, green, energy-efficient and automated. In this paper, a new type of resistence heating forming processes and equipments are designed and manufactured to solve the problem of surface crack caused by the poor room temperature plasticity index of the 5A90Al-Li alloy. The high temperature formability and resistence heating properity of 5A90Al-Li alloy have been studyed in this paper to determine appreciate forming temperature, heating current densit y and other process parameters, meanwhile the resistence heating forming equipments of 5A90Al-Li alloy stringer have been designed and manufactured to fabricate the components which meet the quality requirements.In order to study the formability of the 5A90Al-Li alloy, the room-temperature and high temperature tensile test of 5A90Al-Li alloy test specimen have been experimented. The results indicated that comparing with the relatively low room temperature plasticity index, high temperature can improve the forming limit of 5A90Al-Li alloys to obtain large deformation observably. In addition, the results showed that the strain rate have little influence on the elongation when the deformation taking place within the range of comparatively high strain rate. At the meantime, the resistance heating time-temperature curve of the 5A90Al-Li alloys have been obtained which was based on the resistance heating test. The curve indicated that the heating rate was faster and the balance temperature was higher with the incease of the heating current density. According to the study of resistance heating and heat preservation test of the 5A90Al-Li alloys, we could draw a conclusion that the larger current density would lead to more inhomogeneous temprature distribution of the sheet and longer time to reach balance temperature. Based on the summary and analysis of the experiments, we could obtain the reasonable resistance heating forming parameters of 5A90Al-Li alloys including the forming temperature, stamping velocity, heating current density and current loading path.According to the characteristic of the resistance heating forming process, the new resistence heating forming equipments of 5A90Al-Li alloy stringer have been designed and manufactured, which was mainly targeted at the problem of insulation, the problem of clamping and releasing of the heating sheet, the problem of how to integrate resistance heating and stamping process and the problem of how to realize the automation of the forming processes.Based on the simulation of the forming process of the 5A90Al-Li alloy stringer, the feasibility of the workpiece forming has been discussed and the possible problems during the forming process have been predicted and analyzed. The 5A90Al-Li alloy stringers satisfying the quality standard have been obtained by using the forming parameters determined by experiments and the resistance heating forming equipments. Meanwhile the influence of the temperatuer and the lubricating conditions on the forming quality of the 5A90Al-Li alloys stringers combined with key parts’ thickness distribution of the stringer have been discussed and analyzed.