Crn Thin Films Of Mg-li Alloy Surface Preparation And Research

Magnesium-lithium alloy is the lightest metal material, with excellent properties, such as low density, high specific stiffness and strength, with good shock absorption ability, etc. It is widely used in the automotive, aerospace and microelectronics and many other fields. However, its poor corrosion resistance has hindered the wider use of Magnesium-lithium alloy. At present many researchers make the survey about corrosion resistance on Mg-Li alloy, the surface treatments are: physical methods, chemical conversion coating, chemical plating ,anodic oxidation treatment, and so on. Magnetron sputtering is the main method for the industrial application of film owing to its high deposition rate, simple process, and good film quality and environmentally friendly.In this paper, we used magnetron sputtering to prepare CrN coatings on Mg-Li alloy. The influences of deposition parameters were analyzed, such as nitrogen flow; substrate temperature and sputtering power on the properties and structure of the coatings and the preparation technological parameters were optimized. Using the optimized technological parameters deposited CrN/ZrN multiple coatings and compared with both Single-layer CrN films and ZrN films. X-ray diffraction (XRD), Scanning electron microscope (SEM), and Atomic formic microscope (AFM) were used to characterize the phase structure and the surface morphology of the coatings. Electrochemical methods and Hydrogen evolution experiment were applied to study the corrosion behavior of these coatings. In addition, their corrosion mechanism was analyzed .The main results include:(1)During the preparation of the CrN coatings, there was only one optimal parameter for nitrogen flow, deposition temperature and power. Too higher or too lower these parameters would lead to worse coating properties. Coatings'anti-corrosion property was decided in the coatings defects, pore density and adhesion between coatings and matrix; in single parameter factor experiment, anti-corrosion property of the coatings was the best when nitrogen flow, deposition temperature and power was 20sccm,100℃and 200W.(2)Both CrN coating and ZrN coating prepared with sputtering technique had a developed columnar microstructure and existed preferred orientation.(3)CrN coating had a better protection for Mg-Li alloy than ZrN. The defects which formed in the deposition process were the main sites for corrosion. The evolution of hydrogen which took place at these defects accelerated the damage of the coating. Finally, it led to the failure of the coating/substrate system.(4)CrN/ZrN coatings were dense in a microcosmic scope. The (111) texture of CrN layer was strongly strengthened in CrN/ZrN coating compared with that in CrN coating.(5)Corrosion test indicated that multiple coatings had better protection effect than monolayer. The defect in PVD coating was a short cut for corrosion and the failure of the system was determined by the enlargement of corrosion sources. Therefore, the corrosion failure of the system was considered as a kind of short circuit corrosion behavior.