Evolution Of Defects In Recycle Aluminum Alloy Sheet During Stamping Process And The Improvement Method Of Stamping Formability

The recovery and recycling of aluminum alloy materials will be a reality that the automotive industry must face in the near future.Use at the same level is the goal of recycled aluminum alloy.However,restricted by aluminum alloy melting process,special lubricant and forming process,domestic recycled aluminum alloy can not meet the need of the whole industry application.The utilization rate of recycled aluminum alloy in China’s industry is far lower than the global average,and most of the recycled aluminum alloy can only be degraded.These are due to the lack of in-depth study on defect evolution behavior,stamping lubrication mechanism and stamping process in the stamping process of recycled aluminum alloy sheet.This paper focuses on 6061-T6 deformed aluminum alloy plate.Based on the systematic characterization of the shape,distribution and density of surface defects of recycled aluminum alloy plate,the surface defects of recycled aluminum alloy plate are classified;Combined with in-situ tribological test and modern surface analysis methods,the influence mechanism of various defects on the tribological properties of recycled aluminum alloy was revealed;The solid lubricant suitable for stamping forming of recycled aluminum alloy sheet was developed by compound screening of the composition,content and adhesive composition of lubricating materials;based on the research results of surface roughness and formability of recycled aluminum alloy parts under the condition of solid lubricant,the stamping lubrication mechanism of solid lubricant materials and the influence of recycled aluminum alloy defects on sheet formability are clarified.On these bases,the relationship between stamping process,defect evolution and the formability of recycled aluminum alloy was explored.In the face of key common problems in the stamping process of recycled aluminum alloy sheet,this paper enriches and consummate the stamping theory of recycled aluminum alloy sheet through the research on the failure mechanism,lubrication technology and forming technology of recycled aluminum alloy sheet,so as to provide technical support for the realization of automobile lightweight and the national vision of "carbon harmony".Based on the above research work,the main conclusions of the paper are as follows:(1)Aluminum alloy plate defects are divided into four categories: casting impurity defects,cavity defects,second phase defects and surface rolling defects.Among them,the size and density of casting impurity defects,cavity defects and second phase defects in recycled aluminum alloy plates are significantly higher than those in primary aluminum alloy plates.The influence weight of various defects on plate properties is defined.Among them,casting impurity defects,cavity defects and surface rolling defects have a little effect on the tribological properties of the plate,and most of the defects can be consumed or filled by wear debris with the extension of wear time;the iron-rich second phase defects will be broken in the process of friction and wear,and form a plow ditch on the surface of the soft aluminum alloy matrix..(2)The influence weight of physical and chemical properties of solid lubricating materials on stamping and forming performance of plate is expounded.In order to optimize the stamping forming performance,the thickness and bonding force of solid lubricating materials should be controlled within a reasonable range(thickness <30.0 μm.Binding force >1.0MPa);The dispersion of lubricating medium in different adhesives has a key impact on the stamping lubrication performance of solid lubricating materials.The addition of wetting dispersant can significantly improve the surface energy of PTFE particles in the lubricating medium,so as to improve its dispersion in the adhesive,and finally reduce the friction and maximum punching pressure of aluminum alloy sheet in the stamping process.On this basis,the lubrication model of the solid lubrication film in the forming process is established.It is found that the adhesive in the solid lubrication film can form a shear transfer film on the die surface to protect the die surface.With the migration of adhesive to the die surface,the lubricating medium PTFE begins to precipitate in the interface,which effectively reduces the friction coefficient during sheet forming.(3)It is found that the main factors affecting the formability of recycled aluminum alloy sheet are second phase defects and cavity defects.Among them,the second phase defect gradually deforms,breaks and falls off along the tensile direction with the cup punching process;with the progress of cup punching process,deformation and crack initiation gradually occurs along the tensile direction.The use of solid lubricating materials can effectively alleviate the adverse effects of obvious furrows on the surface of softer aluminum alloy sheet after the second phase defects break and fall off in recycled aluminum alloy,but the adverse effects of cavity defects on sheet formability cannot be restricted.(4)The effect of forming process on the stamping formability of recycled aluminum alloy sheet was studied.It is found that the blank holder force and cup punching speed have an impact on the formability of recycled aluminum alloy sheet: the maximum punching pressure of recycled aluminum sheet increases with the increase of blank holder force,the roughness increases and the surface quality decreases.Different from the original aluminum alloy sheet,the lubricating material selected in the forming process of recycled aluminum alloy should have better film-based bonding force.When the solid lubricating film or stamping oil with poor adhesion is applied to regenerated aluminum alloy,the slower forming speed should be selected.