| With the goal of"double carbon",the application of lightweight equipment and light metal materials has become the focus of the world’s manufacturing industry.Magnesium alloy has shown obvious advantages and strong development potential in many applications of lightweight materials.But the poor corrosion resistance of magnesium alloy,seriously limit the promotion of magnesium alloy.The surface film or coating formed on the surface of magnesium alloy can effectively improve the corrosion resistance of magnesium alloy,but the surface oxide layer of magnesium alloy and the defects existing on the surface of magnesium alloy substrate will affect the generation of the surface film or coating of magnesium alloy.Therefore,the preparation of an effective corrosion-resistant layer on the surface of magnesium alloy requires its substrate to have ultra-high surface accuracy and quality.Chemical mechanical polishing as a processing method that can achieve global or local flattening of the material,the polished magnesium alloy surface precision,can fully meet the magnesium alloy into a film or coating of magnesium alloy surface roughness requirements.For magnesium alloy chemical mechanical polishing research is less,after polishing magnesium alloy surface roughness is high for about 10 nm,can not meet the requirements of magnesium alloy surface film.The polishing solution is mostly alkaline polishing solution with low material removal rate and low processing efficiency.For magnesium alloy chemical mechanical polishing process parameters are studied more for single-factor experiments,ignoring the interaction between each process parameter.Therefore,it is still of great practical importance to study the new polishing solution for magnesium alloy,explore the parameters of chemical mechanical polishing process of magnesium alloy,reduce the surface roughness of magnesium alloy after polishing,and improve the material removal rate of magnesium alloy.In this thesis,the chemical mechanical polishing solution for magnesium alloy was used as the research direction,and the composition and polishing process parameters of the polishing solution for magnesium alloy were optimized through single-factor and response surface experiments,including the type,particle size and concentration of abrasive,the type of p H adjuster,the p H of polishing solution,the type and concentration of corrosion inhibitor,and the polishing process parameters such as polishing pressure,polishing disc speed and polishing solution flow rate.The polishing solution composition was optimized,and the optimal composition of the polishing solution was determined as follows:Al2O3 abrasive with 20 nm particle size and 6 wt.%concentration,malic acid as p H adjuster,polishing solution p H=6,sodium benzoate as corrosion inhibitor with 1 wt.%concentration,and deionized water as the remaining components.In this polishing solution,malic acid is found in nature,and sodium benzoate is a food additive with its own preservative effect.Therefore,the formulated chemical mechanical polishing solution is non-polluting to the environment and non-hazardous to the operator.The polishing process parameters were optimized,and the optimal polishing process parameters were determined as follows:the light pressure was 33 k Pa,the speed of polishing disc was 104 r/min,and the flow rate of polishing solution was 12 m L/min.Using the optimized polishing solution and process parameters for polishing,the surface roughness of magnesium alloy after polishing was able to reach Ra 3.712 nm,and the material removal rate was able to reach 6.63μm/min.The high quality and high efficiency of chemical mechanical polishing of magnesium alloy was achieved.In order to investigate the role of each component of the new polishing solution in the process of chemical polishing of magnesium alloy,the mechanism of chemical mechanical polishing of magnesium alloy was investigated using X-ray photoelectron spectroscopy,scanning electron microscopy,and energy spectrometry.According to the theory of soft and hard acid-base,benzoate ion belongs to hard base,magnesium ion belongs to hard acid,hard acid and hard base are easy to generate salt or complex.In the polishing process,a complete layer of passivated oxide is formed under the action of corrosion inhibitor sodium benzoate to cover the surface of magnesium alloy,which isolates the magnesium alloy substrate from the corrosive medium and prevents the magnesium alloy from further corrosion.The Al2O3 abrasive in the polishing solution will remove the softened layer on the surface of magnesium alloy by mechanical action under the action of pressure and rotational speed.So on and so forth cycle,until the oxidation layer on the surface of magnesium alloy is removed,bare the smooth surface. |
