Mechanism Of Nanosecond Laser Induced Coloring On Stainless Steel Surface And Influence Of Material Thickness On Coloring

As a new surface treatment technology,Laser marking is rapidly replacing traditional marking methods such as imprinting and inkjet,and become another new star in the field of barcode identification.But laser marking can only produce gray or black monochromatic marking.In the field of barcode identification and product decoration,people prefer color patterns.Laser coloring technology came into being,but it is not mature,and the low repetition rate and poor stability are the fundamental factors restricting its development.The influence of laser processing parameters and processing environment on color repeatability and stability has been studied by domestic and foreign scholars.Although some breakthroughs have been achieved,the color produced can not be controlled accurately.This paper takes AISI304 stainless steel as the research object,and studies the coloring from the aspects of laser coloring mechanism,oxide species and distribution,the influence of sample thickness on color,and the simulation of sample temperature field.The specific contents are as follows:Based on nd:yag nanosecond laser marking machine,the dye test was carried out on 304 stainless steel surface.The results show that when the laser power increases in a certain range,the sample surface will show five colors,namely yellow,blue,red,green and brown;The change of sample thickness will have a significant influence on laser coloring.The larger the difference between the two samples with the same processing parameters,the more obvious the color difference is.The mechanism of color formation of nanosecond laser oxide film was studied.The paper selects five typical colors of yellow,blue,red,green and brown to analyze the material composition and relative content of oxide film,and proposes the coloring mechanism of interference color as the main intrinsic color.Although the intrinsic color of oxide has a certain contribution to the color,the color after processing is mainly interference color.The concept of multilayer oxide film is proposed.It is considered that the oxide film produced on stainless steel surface under nanosecond laser is not a single and uniform layer,but two or even multi-layer oxide film composed of different materials.The structure of the double layer oxide film with inner layer manganese dichromate and outer layer of iron trio4 is proposed.The model of thin film interference based on double layer oxide film is deduced by using the principle of film interference.The model is not only the inheritance of the theory of interference color formation of oxide film,but also the further development of the model.The influence of substrate thickness on the surface coloring of 304 stainless steel induced by nanosecond laser was investigated.The color lag and color advance caused by the thickness of the substrate are further studied.The corresponding relationships among sample color,surface temperature and oxide film thickness were established by SEM and EDS.Finally,based on the multi physical field finite element simulation software COMSOL multiphysics,the thermal simulation of the processing process is carried out,and the temperature field of the two phenomena is simulated.The causes of the two phenomena are analyzed from the perspective of heat transfer and the influence of thickness on laser oxidation coloring is summarized.