Study On Effect Of Incremental Shrinking Forming Process On Performance And Microstructure Of Aluminum Alloy Components In High-speed Trains

By means of its many advantages such as less pollution,low consumption,high velocity,safety and convenience,high-speed trains have become one of the important conveyances for humans.Since the lightweight of high-speed trains can decrease the line damage,decline the energy consumption and improve the train braking performance,it is of great practical significance to research on the lightweight materials for high-speed trains.Aluminum alloys have low density,high specific strength,good plasticity and corrosion resistance,which is one of the lightweight materials commonly used in the high-speed train body structure.The aluminum alloy components in the high-speed trains are generally deformed by the bending forming process.However,the conventional bending forming technology has poor flexibility,high development cost and long die production cycle,resulting in a certain restriction for its application.In contrast,the incremental shrinking forming process is highly adaptable and flexible,so as to better meet the market demand for product diversity and rapidity.Therefore,the process has high economic value and broad development prospect in the field of aluminum alloy processing.In this work,the Kraftformer cold forming machine was used for the incremental shrinking forming of 6082-T6 and 5083-H111 aluminum alloys in the high-speed trains.The relationship between the performance and the microstructure of the formed parts was investigated by microhardness test,uniaxial tensile test,metallographic microscope?OM?observation,scanning electron microscope?SEM?observation and electron backscatter diffraction?EBSD?observation.The main research contents and conclusions of this paper are as follows:?1?Under the condition of ensuring the same process parameters,the effect of the incremental shrinking forming on the mechanical properties and microstructure of 6082-T6aluminum alloy were studied.Firstly,the mechanical properties of the formed part were tested by microhardness test and uniaxial tensile test,wherein the uniaxial tensile test sampling was carried out along the rolling direction?RD?,the incline direction?ID?and the transverse direction?TD?of the aluminum alloy sheet,respectively.The results showed that the main strengthening mechanism of aluminum alloy 6082-T6 during the incremental shrinking forming was the work hardening.After the incremental shrinking forming,the microhardness of 6082-T6 aluminum alloy was increased by 8.78%,the tensile strength??_b?and yield strength(?_0.2)were also enhanced by 2.26%and 2.72%,respectively.However,the fracture elongation???was reduced by 31.67%,and the anisotropy of the mechanical properties was also weakened.In addition,before and after forming,the samples in the TD direction had the highest tensile strength??_b?and yield strength(?_0.2),as well as the lowest fracture elongation???.Nevertheless,the tensile strength??_b?and yield strength(?_0.2)of the samples in the RD direction were the lowest but the fracture elongation???was the highest.Subsequently,the microstructure and microtexture of the formed part were studied by means of OM,SEM and EBSD observations.The results showed that,after the incremental shrinking forming,the grain size of the sample was decreased and the number of the crystal grains was increased,but the grain refinement phenomenon was not obvious.There were mainly{011}<100>Goss texture and{112}<111>Copper texture in the6082-T6 aluminum alloy before forming,and the average of Schmid factor was 0.4734.A small amount of{011}<211>Brass texture was also appeared in the 6082-T6 aluminum alloy after forming.The texture orientation was more concentrated and the average of Schmid factor was 0.4668.Finally,by observing the fracture morphologies of the tensile specimens after forming,it was known that the dimple number was reduced,the dimple size was also decreased,and the dimple depth was shallower.In addition,the fracture morphologies of the tensile specimens in the ID direction and in the TD direction had the obvious directionality and presented an opposite trend.?2?The process parameters of the incremental shrinking forming mainly include the stroke feed and the stroke frequency.According to the principle of control variable method,one of the process parameters was guaranteed to be invariable.The effect of the other process parameter on the mechanical properties and microsturcture of 5083-H111 aluminum alloy after the incremental shrinking forming was studied,and the optimal combination of the process parameters was selected.Firstly,under the condition of ensuring the same stroke frequency,the incremental shrinking forming of 5083-H111 aluminum alloy was carried out by selecting the stroke feeds of 34 mm,35 mm and 36 mm respectively.The results showed that the main strengthening mechanisms during forming were the work hardening and the fine-grain strengthening,furthermore the two roles were equivalent.When the stroke feed was constant,the lower the stroke feed,the higher the hardness and strength of the5083-H111 aluminum alloy after the incremental shrinking forming,the worse the toughness,the smaller grain size,and the more the grain boundaries.Then,under the condition of ensuring the same stroke feed,the incremental shrinking forming of 5083-H111 aluminum alloy was performed by selecting the stroke frequencies of 150 times/min,300 times/min and600 times/min respectively.The results showed that the strengthening mechanisms during forming were the work hardening and the fine-grain strengthening,besides the work hardening played a leading role.There was no linear relationship between the stroke frequency and the mechanical properties of this material when the stroke feed was constant.The hardness and strength of the sample were the highest when the stroke frequency was 300times/min.However,there was a linear relationship between the stroke frequency and the grain size of this material.The higher the stroke frequency,the smaller the grain size and the more the grain boundaries.In a word,when the stroke feed was 35 mm and the stroke frequency was 300 times/min,5083-H111 aluminum alloy had the best incremental shrinking forming performance.Through the above research,this paper aimed to predict the performance of aluminum alloys after the incremental shrinking forming,and provide the basic experimental data support and technical guidance for enhancing the quality of the incremental shrinking forming parts,improving the incremental shrinking forming process and solving the practical manufacturing problems.