Effect Of Solution Treatment And Quenching On Strengthening Of 6022 Aluminum In Hot Forming Quenching

With the continuous development of lightweight technology in automobile industry,Hot-Forming-Quenching（HFQ）integrated process for heat-treatable aluminum has attracted attention widely.The process,which combines heat treatment and sheet metal forming,is a complex manufacturing technology.It contains various stages when the process parameters need strict control to obtain high dimensional accuracy and high strengthened parts.Therefore,it is of great significance to study the effect of solution treatment and quenching in HFQ.In this thesis,the mechanical properties and microstructures of the formed parts under different solution treatment and quenching conditions in the hot stamping and quenching process are studied.The morphology,sizes and distribution of the second phases are discussed.The effects of solution temperature,solid solution time and quenching rate on the strengthening effect were analyzed,and the optimum process parameters were determined.Based on the experimental design of CCD（Center Composite Design）,a fitting surface of solution temperature-solution time-tensile strength was established by conducting hot stamping and quenching experiments and the uniaxial tensile experiments,the effects of solution temperature and solid solution time on strengthening was analyzed.The optimal solution process parameters were determined as follows:solution temperature 520℃-550℃,solution time 30min-50min.The effect of different quenching rates on the strengthening effect was investigated after solution treatment at 520℃for 35min,using air,die and water as quenching medium.The temperatures in the resting,punching and holding processes of the sheet was measured by the thermal imager.The cooling rate of the sheet during the punching process was determined to be about 100℃/s-200℃/s and the cooling rate of the U-shape part during the holding process is about 15℃/s-40℃/s.6022 aluminum alloy can be quickly cooled during the range of temperature sensitivity.The morphology and distribution of the strengthening phases in the aluminum matrix obtained after aging were observed by SEM.The effects of different solution treatment conditions and different quenching conditions on the strengthening phase precipitation and distribution were coMPared.It was observed that the solid solution treatment and rapid cooling resulted in the precipitation of a large number of fine dispersed Mg₂Si particles with a diameter of nanometer.Therefore,increasing the solution temperature and quenching cooling rate can increase the concentration of supersaturated solid solution after quenching,which is beneficial to the precipitation of the strengthening phase in the aging process.The effects of different solution temperatures and transfer time on the temperature distribution were analyzed by simulating the temperature fields of HFQ in U-shaped parts in Abaqus.The higher the solution temperature is,the better the effect of the die quenching.Within 7 s,the rapid cooling of the U-shaped parts in the range of temperature sensitivity can be realized.