Study Into The Deep-Drawing Forming Of Aluminum Alloy Sheet Assisted By Electric Current

Aluminum alloy is widely used in industry due to its advantages of light weight and energy saving,but limited by its low plasticity at room temperature and the parts' poor surface quality formed at warm temperature.In recent years,it has been found that materials' plasticity can be improved assisted by the electricity at low temperature.Therefore,the mechanical properties of 2024-T4 aluminum alloy plate and the deep drawing process of the cylindrical part were studied in this dissertation.Firstly,the mechanical properties of the material were studied by uniaxial tensile test without the electricity assistance,the uniaxial tensile test assisted by high-frequency(25hz-100hz)electricity and the test assisted by low frequency(0-0.5hz)electricity,respectively.The constitutive equation was then studied by fitting the curves under the high frequency electricity condition.Secondly,the distributions of electric field and temperature field of the experimental specimens were analyzed by thermal-electric coupling simulation.Based on the simulation results,the deep drawing experiments of the cylindrical parts were carried out under three electrifying modes of "blankholder-die" and "punch-die" was studied.In the end,the microstructure evolution under different electrical parameters was observed and analyzed by the optical microscope and SEM.The results show that: The elongation and flow stress decrease with the increase of electricity density,electricity frequency and electricity pulse width,at the condition of high-frequency electricity.An accurate constitutive relation was obtained by coupling the J-C model with electrical parameters.The average error of this constitutive relation is less than 5%.Under the condition of low-frequency electricity,the elongation increased by 17.6% when the material was pretreated with 50A/mm2 electricity or pretreated with 90A/mm2 electricity and kept for 24 h before tests.For the pre-deformed specimens,the elongation of the material increased by 29.4% at the condition of 110A/mm2 electricity assisted,and increased by 47.6% at the condition of 150A/mm2 electricity.The depth of the deep drawing part increases by nearly 134% when the electricity passes from the blank holder to the lower die.However the deep drawing part is difficult to form by using the electrifying mode of the "punchdie".The dynamic recrystallization was found at the material with the assistance of 150A/mm2 electricity.The grain size of the punched fillet area and die fillet area of the cylindrical part are obviously reduced,and dynamic recrystallization was observed at those area also.