Research On Chemical Mechanical Polishing Slurry And Its Polishing Mechanism Of Aluminum Alloy

Aluminum alloy has the advantages of low density,low cost and good processability,and has been widely used in semiconductor devices,photoelectric imaging and aerospace.Optical aluminum alloy mirrors,as the core parts of precision optical instruments,require nano-level surface roughness,so ultra-precision machining of aluminum alloy is very necessary.In this thesis,chemical mechanical polishing technology is used to polish the surface of aluminum alloy,and atomic-level material removal is realized through the dual coupling effect of chemical corrosion and mechanical grinding,and to obtain an ultra-smooth surface of aluminum alloy with sub-nanometer level surface roughness.Polishing slurry is the key factor of chemical mechanical polishing.According to the published polishing slurry,most of them use corrosive chemical reagents such as strong acid and strong alkali,which brings potential harm to operators and the natural environment.Therefore,it is of great significance to study novel polishing slurry and improve the surface quality of aluminum alloy.The main contents and conclusions of this thesis are as follows:（1）This thesis investigates the effect of each component of the novel polishing slurry（abrasive grains,p H value regulators,oxidizer,corrosion inhibitor）on the chemical mechanical polishing of aluminum alloy by means of single-factor experiment.And according to the experimental results to optimize the polishing slurry parameters,the final determination of the novel polishing slurry composition of aluminum alloy:50nm SiO₂ abrasive grains concentration of 6 wt.%,citric acid adjustment p H=3,H₂O₂concentration of 2 wt.%,1,2,4-triazole concentration of 0.2 wt.%,the rest is deionized water.（2）The influence of polishing process parameters（polishing pressure,polishing pad speed,polishing slurry flow rate）on chemical mechanical polishing of aluminum alloy was investigated by orthogonal experiment and range analysis.According to the experimental results,the process parameters are optimized.The optimized process parameters are as follows:polishing pressure is 24 k Pa,polishing pad speed is 90 r/min,and polishing slurry flow rate is 11 m L/min.The influence on surface roughness is as follows:polishing pad speed>polishing pressure>polishing slurry flow rate;The influence on the material removal rate is:polishing pressure>polishing pad speed>polishing slurry flow rate.Using the optimized novel polishing slurry and process parameters for chemical-mechanical polishing of aluminum alloy samples,the minimum surface roughness of the polished aluminum alloy surface can reach 0.859 nm,and there are no obvious defects such as scratches and corrosion pits on its surface.（3）The interfacial reaction mechanism of chemical mechanical polishing of aluminum alloy was investigated using an electrochemical workstation,X-ray photoelectron spectrometer,Fourier transform infrared spectrometer and Vickers hardness tester.With the increase of citric acid concentration,the corrosion rate of aluminum alloy surface increases.With the increase of H₂O₂ concentration,the corrosion rate of aluminum alloy surface first increased and then decreased.As the concentration of 1,2,4-triazole increases,the corrosion rate of aluminum alloy surface tends to decrease.During the polishing process,H₂O₂ reacts with the surface of aluminum alloy to form an oxide layer mainly containing Al₂O₃,Al OOH and Al（OH）₃.H⁺ionized from citric acid will corrode the oxide layer and generate Al³⁺,which will react with 1,2,4-triazole to form a corrosion inhibition film.With the increase of oxidation degree,the surface hardness of aluminum alloy first decreases and then increases,that is,the material removal first increases and then decreases.（4）According to the interface reaction mechanism of chemical mechanical polishing of aluminum alloy,it is known that the ultra-smooth surface of aluminum alloy can be realized by the synergistic effect of mechanical removal of abrasive grains and corrosion and dissociation of chemical reagents,and the interface reaction process of“H₂O₂ oxidation-citric acid corrosion-1,2,4-triazole corrosion inhibition-SiO₂abrasive grains removal”is put forward.