Experimental Study Of Machining Array Micro-dimples On Magnesium Alloy By Through Mask Pulsed Electrochemical Machining Method

Compared with ordinary superhydrophobic surfaces,the superhydrophobic surface with special structure can effectively reduce the solid-liquid contact time,thereby increasing its application potential in the anti-icing field.At present,such structures having such characteristics are mainly columnar or tapered arrays,and the single structure size is less than500?m,the height ratio is very large,and there are problems such as low efficiency and high cost in the preparation process.In the early stage,through simulation,our research team found that the superhydrophobic surface with hemispherical array structure can also reduce the solid-liquid contact time during droplet collision.Because the mold copying process has the advantages of high efficiency,low cost,and suitable for large-area preparation,how to construct the array micro-pit structure has become a difficult point of research.In this paper,using magnesium alloy as the metal substrate,the combination of COMSOL simulation and experiment is used to study fabricating micro-dimples array by through mask pulsed electrochemical machining(TMPECM),to investigate the regulation of the microstructure parameters of magnesium alloy-based micro-pits array,and to study the droplets collision on the superhydrophobic surface to verify the effect of the solid-liquid contact time reduction.The main research work and results of the thesis are as follows:(1)The multiphysics finite element model of through mask pulsed electrochemical machining process was established by COMSOL.The actual machining conditions were simplified reasonably,and the boundary conditions for simulation analysis were obtained.Firstly,the interaction law between structure change and field strength distribution during processing was analyzed.The variation of micro-dimple's structure with current density and processing time is revealed.Then,by analyzing the electric field distribution in the machining gap,the distribution of current density on the anode surface is derived,and the reasons for the formation of the micro-pit morphology are explained.Finally,the temperature field distribution in the machining gap is analyzed,and the temperature curve during the processing time is obtained.(2)Based on the above simulation results,through mask pulsed electrochemical machining experiment of the micro-dimples array was carried out.According to the test requirements,the design and manufacture of the side punching fixture were completed,and the design of the pulsed electrochemical machining test system was carried out.Through the preliminary comparison experiment of different mask materials,the thickness of the mask is thicker and the shielding effect is better.The photoresist dry film is used as the experimental mask material,and the preparation parameters of the mask are determined.Through mask pulsed electrochemical machining experiment is carried out to investigate the processing time,current density,power supply duty ratio and frequency for the shape of the micro-dimples structure influences.Finally,the experiments with the condition of 0.8 mm for the mask pattern's diameter,10 A/cm~2 for the current density,75 s for the time,30 kHz for the pulse frequency,30%for the duty ratio,15%for the electrolyte concentration,can get the array micro-dimples whose average diameter is 1.56mm,average depth is 0.82 mm on the AZ31B magnesium alloy.(3)Based on the micro-dimples array fabricated by through mask pulsed electrochemical machining,a hemispherical array structure with a diameter of about 1.56 mm,a height of about0.82 mm and a pitch of about 0.19 mm was obtained by pouring replication using PDMS polymer.The superhydrophobic nanoparticles were further sprayed to obtain a superhydrophobic hemisphere array structure.Through the droplets'collision test,it is found that when the Weber number We?7.94,the solid-liquid contact time is greatly reduced,which is nearly 47.7%contact time of the ordinary superhydrophobic surface.It proves that using superhydrophobic surface with the hemispherical array structure has reducing contact time effect.