Research On The Mechanism And Application Of Ultra-smooth Metal Foil Manufactured By Laser Shock Polishing

As the market for military and consumer electronics continues to expand,miniaturization of electronic products has become an important trend in industrial manufacturing,where high quality metal foils with excellent properties are widely used.High-quality metal foil surface finish has great impact on its function,appearance,and frictional properties in various applications.Therefore,it is necessary to polish the surface of sheet metal to reduce its roughness.In this thesis,based on the analysis of existing polishing techniques at home and abroad,a new laser polishing technique is proposed as a general method for metal foil surface polishing with reference to laser shock forming technology,aiming to significantly reduce the surface roughness of metal foil while improving the comprehensive properties of metal foil.In this thesis,the crystallographic features and microstructure evolution of aluminum foil before and after laser shock polishing are systematically analyzed by taking laser shock polishing of metal foil(the case of aluminum foil)as the main line,various properties characterization methods,modern analytical testing techniques and molecular dynamics simulations,and the mechanism of laser shock polishing to reduce the roughness of aluminum foil and improve its comprehensive properties as well as the nanoscale ultrafast dynamic process of laser shock polishing are determined.The main contents of this thesis are as follows:Firstly,the necessity of metal foil surface polishing is systematically summarized.Both traditional polishing techniques and or non-traditional polishing techniques still have the limitations of tedious steps,the need for cleaning,and unstable polishing effects that greatly reduce efficiency.Therefore,in view of the shortcomings of commonly used polishing technology,this thesis puts forward a new solution,namely laser shock polishing technology.This polishing method not only does not produce grinding debris but also polishes uniformly and is suitable for ultra-smooth polishing of foil metals.In addition,the polishing method does not need complicated steps such as cleaning,which greatly improves the polishing efficiency.Secondly,the basic principle of laser shock polishing technology,process parameter adjustment,experimental scheme and analysis ideas are introduced in detail,and the influence of process parameters on the polishing technology is studied.Next,the observation of the surface morphology of aluminum foil shows its process superiority.The experimental results show that for the laser shock polishing technique,the polishing effect is better after applying temperature assistance(whether temperature is applied or not is called SWLP and SLP,respectively);the polishing effect is better with high laser energy than with low energy;the polishing effect is best for the large-area SWLP-treatment with 1 J laser energy,the surface roughness of aluminum foil is reduced from 148 nm to 3.7 nm,which is 97.5%.The extended experiments also show that the laser shock polishing technology is suitable not only for the polishing of aluminum foil,but also for other metal foils.Thirdly,the micro-tensile test,nano-indentation test and electrochemical corrosion test show that the laser shock polishing technology can significantly improve the comprehensive properties of aluminum foil.The experimental results show that the SWLP experiments at 1 J laser energy resulted in a 37.9% increase in tensile strength and 33.2% decrease in elongation;32.0% and 25.2% increase in nano-hardness and elastic modulus,respectively;and 65% decrease in corrosion rate of aluminum foil.Good property is a necessary condition for the preparation of some electronic components as the main body and template,so SWLP technology is of great significance.Fourthly,by combining the results of the molecular dynamics simulation,transmission electron microscope and electron backscatter diffraction technique,the polishing mechanism of laser shock polishing on the surface of aluminum foil is clarified through the evolution of microstructure and crystallographic features of aluminum foil.After laser shock polishing,the initial arrangement of aluminum atoms changed,high stress and high strain regions appeared,a great many dislocation structures such as dislocation cells,dislocation walls and dislocation entanglement appeared in the aluminum foil,and the dislocation density increased significantly.The plastic deformation mechanism of aluminum foil is mainly dislocation slip,supplemented by a few stacking faults to accommodate the plastic deformation.The dislocations in the aluminum foil gather around Fe particles,and the entanglement of the Fe phase and the dislocation produces the pinning effect.The improvement of tensile properties of aluminum foil after SLP/SWLP is mainly due to high-density dislocation and pinning effect.During the plastic deformation of aluminum foil,the dislocation structure gradually changes from random dislocation → dislocation line→ dislocation tangle → subgrain boundary;eventually,rarely refinement is completed for the whole.After SLP/SWLP,the distribution of misorientation angles of aluminum foil concentrates in low-angle boundary.SLP/SWLP also markedly affects the distribution of texture,primarily the change of cubic texture.Both SLP and SWLP benefit by strain hardening and pinning effect caused by plastic deformation,but SWLP produces larger plastic strain and faster dynamic precipitation,resulting in denser dislocation structure density,and denser nano precipitates respectively.Therefore,the dislocation structure in sample after SWLP-treatment is more stable.Finally,the application of SWLP technology-laser shock nanoimprinting is investigated.SWLP not only enables the surface morphology of the aluminium foil to meet the requirements of the LSI process,but also results in higher moulding accuracy,integrity and uniformity of the aluminium nanostructures obtained by LSI.In addition,the SWLP treatment also results in less damage to the aluminium nanostructures during the demoulding process after LSI,significantly reducing the residual aluminium foil inside the silicon mould nanostructures,which may affect the secondary use and service life of the silicon mould.Comparison of various polishing methods,analysis of surface morphology and comprehensive properties of the laser shock polishing technique as well as analysis of ultrafast dynamic processes at the nanoscale,crystallographic features,microstructure evolution,fundamental differences between SLP and SWLP and the significant enhancement of LSI performance by SWLP.All shown that this thesis not only provides a new technology for metal foil surface polishing,but the explanation of plastic deformation of aluminum foil and laser polishing mechanism in this thesis also provides some basis for the future proposal of other polishing methods and the understanding of their polishing/material modification mechanism.There are 47 figures,3 tables and 125 references in this thesis.