| In recent years,the application of lightweight material in transportation vehicles has become one of the important directions to reduce fuel consumption and emission.Aluminum alloys,with the advantages of low density,high strength-to-weight ratio,good corrosion resistance and good recyclability,can be well applied to lightweight vehicles,especially for body panels.However,the formability of aluminum alloys panel is limited at room temperature.The warm stamping and hot stamping technology can enhance formability of material and expand its scope of application.Warm punching generally refers to the isothermal forming in low temperature.During hot stamping,the blank was firstly heated to temperature of solution heat treatment and kept at the temperature for a period of time.Then,the hot blank was moved to dies for deformation.The part was quenched in the dies,followed by ageing process to improve the strength.While the blank was heated to 200-300? before deformation during its warm stamping.The two technologies are employed to manufacture aluminum alloy parts and it can improve material forming ability compared to cold stamping,but there are not enough research on 6014 Aluminum Alloy especially the influence of forming parameters to the stamping quality.Thus,the application of 6014 aluminum alloy on transportation vehicles is limited.In this paper,the formability and forming process of 6014 aluminum alloy are studied by means of experiment and simulation.The tension experiment,solution treatment experiment,bending and drawing experiment,et al.were done to study the influence of technology parameters to the formability and strength of 6014 aluminum alloy.The analytical methods of microscope(OM),scanning electron microscopy(SEM),electron backscatter fiffraction(EBSD)and X-ray diffraction(XRD)were used to observe the fracture morphology and microstructure.Based on the tensile test at different temperatures and strain rates,a constitutive equation using up-dated Fields&Backofen equation and a modified Arrhenius model which is a hyperbolic sinh function including the deformation activation energy and deformation temperature were established to describe the relationship of true stress with true strain under different temperatures.The model can accurately present the thermal behavior of 6014 aluminum alloy.The heat treatment process of 6014 aluminum alloy in hot stamping was studied by heat treatment experiment.It mainly focused on the influence of solution temperature and time,artificial aging temperature and time on the final quality of specimen.The mechanism of heat treatment on the mechanical properties of 6014 aluminum alloy was studied with the microstructures observed by scanning electron microscope.The optimization algorithm was employed to obtain optimal process parameters.The factors affecting the thickness and the springback of the parts were investigated including initial blank temperature,blank holder force and the holding time using the bending experiments.The finite element model was established and proved by the results of the experiments.The equation of the springback and different parameters were established with the results of the simulation using the methods of mathematical statistics.The experiments and simulation of cross-part drawing were carried out to study the formability of 6014 aluminum alloy under different temperature.The forming defects and damage crack mechanism were analyzed.The influence of process parameters on the forming minimum thickness of hot-stamped part was quantified using mathematical statistics. |
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