Analysis Of Rheological Behavior For AA7N01 Used In High-speed Train And Research On Extrusion Process Of An Draw Beam Profile

In recent years,with the challenges of ecological problems such as environmental pollution and resource shortage,green manufacturing and energy conservation and emission reduction have become the important part of global sustainable development strategy.In the transportation industry,lightweight car body is one of the inevitable choices to save energy and reduce emissions.As a typical Al-Zn-Mg high-strength and hard aluminum alloy,AA7N01 is widely used in the bearing structure of high-speed train to meet the requirements of lightweight design with the advantages of low density,high specific strength and excellent corrosion resistance.However,there are many difficulties in the extrusion process and profile quality control of the alloy due to its poor fluidity.Therefore,in order to develop reasonable extrusion parameters and ensure good profile quality,it is necessary to comprehensively analyze the high temperature rheological behavior and thermal processing properties of AA7N01.In addition,the porthole extrusion and the piercing extrusion are the two main extrusion processes in the actual production of hollow aluminum alloy profiles.Compared with the former,there is no metal dividing and welding during the piercing extrusion,which can avoid welding defects and improve the finished product rate.The piercing extrusion is mainly used in the production of seamless hollow aluminum profiles.In this work,the AA7N01 used in high-speed train is chosen to investigate the constitutive model,processing maps and extrusion process by numerical simulation coupled with experimental analysis.The main research works are as follows:(1)A new idea for identifying the material parameters in the constitutive model was proposed.Based on the true stress-strain data with double-correction of friction and temperature,the two-step inverse analysis method was used to obtain the friction coefficient during hot compression and the material parameters in strain-compensated Arrhenius-type constitutive model of AA7N01 by minimizing the difference between predicted and experimental shape and force-displacement data,respectively.(2)Based on the dynamic material model theory,the effects of strain on power dissipation efficiency and instability parameters under different temperatures and strain rates were studied and the processing maps of AA7N01 was established.Through the analysis of hot compressed microstructure and the construction ofdynamic recrystallization model,it was found that strong dynamic recovery and a small amount of continuous dynamic recrystallization were the main softening mechanisms of AA7N01 and high temperature and strain,low strain rate were beneficial to the occurrence of dynamic recrystallization.(3)The numerical simulation of porthole extrusion and piercing extrusion for AA7N01 draw beam profile were carried out to study the characteristics of the above two extrusion processes with HyperXtrude software.And the extrusion experiments were carried out to verify the accuracy of constitutive model and numerical model.In addition,it was founded that grain morphology and texture distribution varied with different positions on the cross-section of piercing extrusion profile,but the difference in mechanical property was not obvious.