Research On Electrically-assisted Hot Forming-die Quenching Integrated Process Of 2195 Al-Li Alloy

In recent years,the demand for lightweight parts in the aerospace field has become more and more urgent.Al-Li alloy has become a promising structural material because of its advantages of low density,high modulus of elasticity and specific strength.However,Al-Li alloy has problems such as poor formability at room temperature,large rebound,and thermal distortion in heat treatment,which severely limit its application.In this paper,pulse current is introduced on the basis of the conventional hot forming-die quenching process.On the one hand,it integrates hot forming and heat treatment to solve the above problems.On the other hand,the introduction of pulse current has shortened the process and greatly saved energy consumption.In this paper,the influence of pulse current on the heating,solution treatment and forming process of 2195 Al-Li alloy sheet is studied,which lays the foundation for the development of Al-Li alloy electrically assisted hot forming-die quenching integrated process.Aiming at the problem of nonuniform temperature distribution of the plate during the resistance heating process,a sample with a shape of "narrow sides" was designed.Combining finite element analysis and experiment,the effect of the width of end and clamping distance on the steady-state temperature distribution was analyzed.The results show that the reduction of the width of end and the clamping distance will enhance the heat generation at the end and improve the uniformity of the temperature distribution.This idea can be used to solve the problem of uneven temperature distribution when the rectangular plates of various sizes are heated.Resistance heating experiment was conducted to determine the heating parameters of different solid-solution temperature.Compared with the conventional solution treatment,the effect of electropulsing solution treatment on the microstructure and mechanical properties of 2195 Al-Li alloy was analyzed by means of the room temperature tensile test,hardness test and metallographic structure observation.It is found that electropulsing treatment promotes the diffusion process and accelerates the dissolution of the second phase,which has a certain role in promoting the solid-solution process of the sample.The effects of solid-solution temperature and strain rate on deformation behavior of 2195 Al-Li alloy sheet in solid-solution state was studied by high-temperature tensile tests,and the variation of thermal mechanical properties was analyzed.Based on the resistance heating forming process,an ‘electrical-thermal-structural' multi-filed coupling model was established to explore the effects of different process schemes,initial forming temperature,lubrication conditions,and forming speed on the thickness distribution and temperature distribution of "U" shaped parts.The results show that,compared with the conventional HFQ process,the temperature drop of the parts during the resistance heating forming process is smaller,and the formability is better.At the same time,under the premise of ensuring forming and avoiding the quenching sensitive temperature range,appropriately reducing the temperature and increasing the forming speed can improve thickness homogeneity.Good lubrication conditions have great positive effects on the surface quality,thickness distribution of the parts and die life.