Study On Chemical Mechanical Polishing Of Magnesium Alloy And Its Material Removal Mechanism

Magnesium alloy is widely used in the fields of aerospace, aviation and 3C owing to its good mechanical properties. The good properties of magnesium alloy expand its application range in engineering field, such as lightweight, high damping, high thermal conductivity, resistance to vibration, electromagnetic interference, high electro negativity and ease of recycling. However, some appearance defects, such as scratch and wear, are easily formed in the processing of magnesium alloy because of its soft texture and low hardness. In particular, some critical or important precision parts always need to be processed at a very high precision. As ultra-precision processing technology, chemical mechanical polishing(CMP) can achieve the overall planarization of a large flat surface and result in a perfect mirror finish. This paper aims to deeply study the polishing slurry, removal mechanism and technology of the chemical mechanical polishing process of magnesium alloy through theoretical analysis and polishing experiment.Firstly, the impact that polishing medium performed in the chemical mechanical polishing process of magnesium alloy was studied. Combining with the special physicochemical property of magnesium alloy, the polishing medium’s impact on the polishing performance was mainly studied. From the aspects of surface roughness and material removal rate, it was found that: ? The quality of surface finish was highly improved with organic solvent as polishing medium, and the surface pitting was reduced, but the material removal rate is low; ? However, when the polishing medium was deionized water with moderate corrosion inhibitor, the quality of surface finish was improved with few surface pitting and the material removal rate was proper.Secondly, different inhibiters’ impacts on the corrosion resistance and polishing performance of magnesium alloy were studied through static and dynamic experiments. The slow-release effect and principle were concluded from some electrochemical experiments and the analysis of skin covering of the magnesium alloy surface, the best corrosion inhibitor and its proportion were figured out through the comparison of polishing experiments. According to the experiment results, the static slow-release effect and the surface of magnesium alloy reached the best with 1wt% Na2HPO4 as the corrosion inhibitor, so appropriate amount of corrosion inhibitor could improve the polishing quality of magnesium alloy effectively.Furthermore, the main parameters which had an impact on the chemical mechanical polishing of magnesium alloy were optimized and experimentally studied. Based on the chemical and mechanical actions, the effect laws that some elements had on the polishing performance were studied, including the polishing process parameters(pressure of the polishing, speed of the polishing desk, fluid flow rate of the polishing, the polishing time), p H adjusting agents(inorganic bases, organic bases), the type and concentration of the abrasives. The optimum technology parameters were worked out with orthogonal experiment, and then the formulation of polishing solution was optimized through single factor experiment. Finally the chemical mechanical polishing solution of magnesium alloy was prepared.Finally, it was further studied how the mechanical, chemical action and interactions impact on the material removal of magnesium alloy, the microscopic material removal mechanism was analyzed on the basis of two-body and three-body contact slip model of magnesium alloy in the chemical mechanical polishing. According to the results, the mechanical action of the abrasive grains was the major factor in the material removal of magnesium alloy in the chemical mechanical polishing, and the chemical mechanical interaction between abrasive grains and polishing solution could considerably increase the material removal rate of magnesium alloy in chemical mechanical polishing.