Research On Strengthening Mechanism Of Integrated Process Of Quenching-Hot Forming For Aluminium6A02Sheet

Along with the expansion of the energy consumption pressure, weight reductionbecomes the urgent matter, which can be realized by optimized structural design andusage of light materials, such as aluminum and magnesium alloy. In recent years, thedemand for aluminum alloys has increased in response to a growing need forlightweight structural metals, which can be found to gain more and more applications.Efforts have been made to improve the formability and strength of these materials byforming complex-shaped sheet workpieces. Therefore, the new technology combiningstrength and hot forming has been the research hotspots, which can be used tomanufacture high precesion and strength part with mass production.A special device has been established for research on integrated process ofquceching-hot forming, which achieves rapid heating, precise temperature controlling,fast cooling, high pressure gas transmission, control, and reliable seal et al.In this study, the mechanical properties of alumimium6A02sheet was tested byuniaxial tensile test at high-strain-rate and different temperatures. The strain rate was0.1s^-1and the temperature was from R.T. up to575℃. Results show that the totalelongation of the6A02sheet began to increase rapidly after325℃, and reached themaxinum value at500℃. Tensile tests with strain rate ranged from0.001s^-1to0.1s^-1were also carried out at different temperatures ranging from250℃to450℃. Totalelongation decrases with strain rate increasing before300℃, then increases after350℃.The fracture surface was observed after tensile tests at different conditions by SEM. Thedimple fracture can he seen at different temperatures, and the character combininghybrid tough and brittle fracture appears after550℃with strain rate of0.1s^-1and400℃with strain rate of0.1s^-1.Vickers hardness tests were carried out to evaluate the strength change ofaluminium6A02sheet for integrated process of quceching-hot forming, at differentconditions. Materaial softening happens seriously during hot forming. Solutiontreatment plenty is necessary to achieve good strength, whose essence theory is theprecipitation strengthening theory. Solid solubility, aging process and cooling rate werestudied to reflect the strength change of HFQ. At the same conditions, the greatercooling rate, the better strengthening effect during HFQ-cold die forming; The vickershardness of formed part showed a decreasing trend after the increase firstly, with the dietemperature increases during HFQ-hot die forming. Hot foming after water quenchingcan obtain the almost same strength effect as HFQ-hot die forming befroe300℃, then has a decreasing trend with temperature increasing.Precipitated phase was observed and determined by transmission electronmicroscopy （TEM）, the main strengthening phase is Mg2Si. The size of precipitatedphase is relatively small, the parts were under aged. The amount and distribution of thesecond phase were analyzed by scanning electron microscopy （SEM）. The second phaseprecipitated uniformly along matrix, which leads to the strength. The second phaseprecipitated along the grain boundaries and impurity phase precipitated ununiformlyreduce the strengthen effect. The microstructure were analyzed by electron backscatterdiffraction（EBSD）, the main reason for hot forming is recovery.