Research On Material Flow Behavior And Extrusion Die Optimization Design Of An AA7N01 High-strength Beam Profile Used In High-speed Train

In recent years, with the fast development of high-speed trains in China, it is very urgent for the demand of lightweight car body. With the advantages of light weight, high strength, good electrical and thermal conductivity, corrosion resistance, beautiful appearance and easy of recycling, aluminum profiles have become main structure material of high-speed trains. Currently, the chassis of high-speed trains are mainly manufactured by 7N01 aluminum alloy profiles. As is a kind of high-strength and hard aluminum alloy, the extrusion process of AA7N01 is very difficult. However, there are few literatures on extrusion process and die structure design for AA7N01 profiles. At present, there still exist several main problems such as low rate of finished products and short life cycle of die on AA7N01 extrusion process, which limits the research and development of this kind of aluminum alloy profiles to a certain extent. Therefore, it is very urgent to use scientific methods to study the key problems, such as die design, process formulation and products quality control for AA7N01 profiles. However, scientific methods are based on deep understanding of deformation mechanism, constitutive relation, material flow behavior and the effects of process and die structure parameters during AA7N01 extrusion process. The solution of these problems will contribute to the improvement of yield, products quality and die life for AA7N01 profiles.The purpose of this work is to numerically and experimentally study the extrusion process of an AA7N01 beam profile used in high-speed train. Firstly, the mechanics parameters and thermo-physical parameters of AA7N01 ingot are obtained. And the Arrhenius constitutive model to describe the deforming behavior of AA7N01 at elevated temperature is determined by the inverse analysis method. Secondly, the transient simulation of AA7N01 beam profile extrusion is carried out and verified by practical extrusion to investigate the material flow behavior during an entire extrusion cycle. Thirdly, the influences of extrusion process parameters on the product quality, extrusion load and the maximum stress of extrusion die are studied. Finally, the extrusion die structure is optimized using the response surface method and morphing technique. The main research content and results of this work are as follows:(1) The mechanics parameters and thermo-physical parameters of AA7N01 are obtained experimentally. The force-displacement curves under different temperatures and strain rates of AA7N01 are obtained by hot compression tests. Then the material parameters of Arrhenius constitutive model of AA7N01 are determined with the inverse analysis method.(2) Based on HyperXtrude software, the transient numerical simulation of AA7N01 beam profile extrusion is carried out to investigate the material flow and thermal behavior. The practice extrusion process is also realized in the workshop. The nose-end shape of the extrusion profile, the evolution curve of exit temperature and of extrusion load by FE simulation shows excellent agreements with experimental observation, which shows the accuracy of the constitutive model and numerical model.(3) By using Taguchi’s method, the influences of billet diameter, ram speed, die temperature, billet preheated temperature and container temperature on the uniformity of metal flow, extrusion load and the maximum stress of extrusion die are studied. And the optimal process parameters are determined.(4) The response surface method is adopted to optimize the outline and height dimensions of pocket structure. Then by combining the morphing technique, simulation and optimization algorithm, the outline dimensions of pocket structure are further optimized.