Investigation On Contact Heating Technology And Equipment Application On Aluminum Alloy Sheets

As people pay more and more attention to environmental protection and energy,it is particularly important to promote lightweight of automobile to achieve energy saving and emission reduction.The excellent comprehensive performance makes aluminum alloys have broad application prospects in lightweight of automobile.At the same time,the application of hot stamping process for heat-treatable aluminum alloy sheets effectively solves the problems of large springback and poor ductility of high-strength aluminum alloys during forming at room temperature,and expands the application range of aluminum alloys in vehicle parts.The realization of hot stamping process for aluminum alloy sheets is inseparable from the heating process of the alloy sheets to complete the solution heat treatment(SHT)and aging treatment.The contact heating process can solve the problem of low heating efficiency of conventional radiation furnace and improve the efficiency of hot stamping.In this article,a contact heating experiment device was designed and manufactured,based on 7075 aluminum alloy,the heating characteristics of contact heating device were studied,and the influence of contact heating temperature and time on the properties of 7075 aluminum alloy was explored.The precipitation kinetics of??in Al-Zn-Mg-Cu alloy was also studied by phase-field modeling.By finite element simulation,the power and structural parameters of the contact heating device were determined.The effects of the diameter of heating holes,the space between heating holes and the distance from working surface to the heating hole on the temperature uniformity of the device working surface were analyzed.Combined with the principle of heat transfer and control engineering,the contact heating experiment device for aluminum alloy sheets heating was designed and manufactured.The heating characteristics of the contact heating device were studied.It was found that the temperature of the device working surface was lower than the set temperature due to the large heat dissipation by surface radiation and convection.By the contact heating experiments for aluminum alloy sheets,it was found that the device can heat the sheet of 2mm thick to the vicinity of the target temperature within 15 s.And the time required for sheet heating increased slightly as the set temperature increased.The rapid solution heat treatment experiments of 7075 aluminum alloy were carried out on the contact heating device.The effects of the temperature and time during contact heating on the mechanical properties and the microstructure of the aluminum alloy were investigated.The results showed that the contact heating process can shorten the time for SHT of 7075 aluminum alloy to 15-20 s without reduction of mechanical properties.We had also tried to optimize the aging treatment of 7075 aluminum alloy by contact heating method.Combining with paint baking process,the contact heating method was used to pre-age 7075 aluminum alloy at 120 ~oC for more than 2 min,which could effectively reduce the aging time of alloy while losing less mechanical properties.The precipitation kinetics of??phase in Al-Zn-Mg-Cu alloy was studied by phase-field modeling.And the effects of solute diffusion and stress distribution were considered in the simulation,which makes the simulation results more accurate.The modeling results showed that the small diffusion rate of solute elements during aging process limited the growth rate of??.Meanwhile,in the two-dimensional modeling plane,the??precipitates grew in a plate shape,the solutes on both sides of the plate can continuously diffuse to the front of the growth interface,as a result,the growth rate of the??precipitates decreased little with the extension of the aging time.