Microstructures And Mechanical Properties Evolution Of 7075 Aluminum Alloy Processed By Repetitive Continuous Extrusion Forming

Among Al-Zn-Mg-Cu alloys,7075 aluminum alloy is one of the deformed aluminum alloys that can be strengthened by heat treatment.Due to its excellent comprehensive mechanical properties,7075 aluminum alloy can be used as a lightweight and high-strength structural material,and has been widely used in aviation,transportation and construction.At room temperature,the plasticity of 7075 aluminum alloy is relatively poor,so the plastic for ming of this alloy is generally carried out at high temperature.Therefore,by studying the rheological behavior of7075 aluminum alloy at high temperature,it can provide a theoretical basis for formulating the plastic forming process of this alloy.The o riginal material selected in this paper is the 7075 aluminum alloy bar after horizontal extrusion.In this paper,the Gleeble-3500 thermal simulation testing machine is used to conduct a thermal compression test on the original alloy bar.The obtained resu lts were used to study its thermal deformation behavior and microstructure evolution.Then,in this paper,combined with the results of thermal deformation behavior analysis,the repeated continuous extrusion process is simulated and analyzed by DEFORM-3D finite element simulation software.Finally,the actual production is carried out by combining the previous simulation analysis and data,that is,the repeated continuous extrusion test of the original alloy bar at two different speeds is carried out,and then various types of test methods are used to study the repeated continuous extrusion and the combination Microstructure and properties of heat-treated 7075 aluminum alloy.The main findings are as follows:(1)From the true stress-strain curve of 7075 aluminum alloy,it can be seen that in the range of 25～200 °C,the role of the work hardening mechanism of 7075 aluminum alloy material is significantly higher than that of the dynamic softening mechanism.When the temperature is increased to 300 °C,the inf luence of the dynamic softening mechanism becomes greater,mainly the dynamic recovery mechanism.The temperature at 400 °C and 500 °C further strengthens the dynamic softening mechanism,mainly the dynamic recrystallization mechanism.(2)The repeated continuous extrusion process of 7075 aluminum alloy was numerically simulated and analyzed by DEFORM-3D finite element simulation software.The simulation analysis results show that increasing the rotation speed of repeated continuous extrusion from 3rpm to 7r pm will cause greater frictional heat inside the material,and rise to a higher temperature in a shorter time,which may lead to uneven temperature distribution inside the alloy.Different degrees of expansion and deformation,which are more likely to caus e internal cracks in the alloy.(3)The repeated continuous extrusion process can significantly refine the grains of 7075 aluminum alloy.After the third pass of repeated continuous extrusion deformation at a rotational speed of 7 rpm,the grains of the al loy are transformed from the fibrous elongated grains of the original alloy.It is a fine equiaxed crystal with an average grain size of 2.3μm.(4)After the low-speed repeated continuous extrusion of 7075 aluminum alloy undergoes aging heat treatment,the precipitation reaction of the alloy is earlier and more intense.Roughening and transformation.