| As an ideal modern industrial structure material,magnesium alloy has a broad application prospect in automotive,aerospace industry and other fields.It is known as"green engineering material in twenty-first Century".However,magnesium alloy has very high chemical and electrochemical activity,making it easy to oxidize in natural environment and cause corrosion.Therefore,finding an effective way to improve corrosion resistance of magnesium alloys has become a top priority.At present,various surface modification technologies are mainly used for processing.Among these technologies,As a green and environment-friendly film deposition technology,magnetron sputtering has the characteristics of fast deposition rate and high power efficiency.In recent years,it has been highly valued by researchers both at home and abroad,and has made rapid development and widely used in the field of industrial film preparation.Based on the orthogonal design theory,Al2O3 ceramic film was deposited on the surface of AZ31 magnesium alloy by RF magnetron sputtering.The films were characterized by scanning electron microscopy?SEM?,X ray diffractometer?XRD?and metallographic microscope to investigate the influence of sputtering parameters?deposition time,sputtering power and negative bias?on the grain size of the film.The effect of sputtering parameters on the corrosion resistance of Al2O3 ceramic film was investigated by means of electrochemical tests and single factor experiments.The corrosion behavior of magnesium alloy matrix and Al2O3 ceramic film in NaCl solution was studied by means of metallographic microscope,and the corrosion mechanism was analyzed according to the corrosion electrochemical theory.The results of the study show that:?1?Prepared with the deposition time of 60min,the sputtering power of 250W and the negative bias voltage of 80V,the Al2O3 ceramic film is mostly Delta-Al2O3,and there is the preferred orientation in the?020?mask.The Al2O3 ceramic film prepared under this process are thin and transparent,and the thickness of the film is only 3.15?m,and the surface is basically smooth,uniform and dense.There are scattered small particles in the surface of film,which growth mode is island.?2?When the deposition time is 20min,the grain size is relatively large,but with the prolongation of the deposition time,the grain size of Al2O3 ceramic film decreases.With the increase of the sputtering power,the grain size of the Al2O3 ceramic film decreases when the sputtering power is between 100250W,and the grain size of the film increases greatly when the sputtering power is between 250W300W.With the increase of negative bias,the grain size first decreases and then increases.Among them,the Al2O3 ceramic thin film has the smallest grain size when the negative bias is 60V.?3?The corrosion resistance of Al2O3 ceramic film deposited on magnesium alloy varies with the process parameters.When the deposition time is prolonged,the thickness of the film becomes thicker,which makes the film's corrosion resistance better than the matrix,but the long deposition time will cause the thin film to crack.The increase of sputtering power increases the energy of the sputtering particles,but the sputtering particles in high power will etch the film surface,which leads to the defects of the film.The bias pressure can enhance the film forming ability,but the high bias will cause the film quality to decrease.The optimum technological parameters that affect the corrosion resistance of Al2O3 ceramic film is 60min,250W and 40V.Compared with the matrix,the corrosion potential of Al2O3 ceramic film prepared under the process parameters is increased from the-1.630 V to-1.492 V,and the corrosion current density is reduced from 7.455×10-44 A·cm-22 to 5.96×10-44 A·cm-2.?4?Soaking test showed that Cl-easily corroded the loose porous oxide layer,resulting in the accelerated dissolution of the magnesium alloy substrate and a complete corrosion state.While due to the high density of Al2O3 ceramic film,the corrosion medium is effectively hindered,the corrosion is relatively mild,and there are only very shallow corrosion pits appear.The results show that the corrosion resistance of the Al2O3 ceramic film is improved by depositing on the magnesium alloy. |
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