The Growth of Phosphate Coating Layer with Different Zn/Mn Ratio on AISI 4140 Alloy Steel

• Main Authors: CHENG,KAI-HAN, 鄭楷翰
• Other Authors: CHENG,TSUNG-CHEIEH
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/44wa7f

碩士 === 國立高雄應用科技大學 === 機械工程系 === 106 === Phosphate coating is widely used in hand tools, automobiles, marine anti-corrosion, painting and other industries, because the phosphate coating can form a stable and insoluble coating on the metal material, which can effectively as a barrier to block avoid corrosion of metal materials like moisture, oxygen, corrosive substances, etc.Phosphate coating is mainly classified into zinc phosphate coating and manganese phosphate coating. Currently, most of the phosphate coating research focuses on only one kind of each phosphate coating. The study of comparison between zinc phosphate coating and manganese phosphate coating is rare. In this study, we used chemical treatment to grow zinc phosphate, manganese phosphate, and composite phosphate coating on AISI4140 alloy steel. By changing the Zn/Mn ratio in the phosphating solution, different zinc/manganese ratio of composite phosphate coatings were grown. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) were used to analyze the surface morphology, element content, coating structure. Spectrophotometer was used to analyze its optical properties, and coating weight was measured by removing it from metal surface using chromic acid in order to determine the effect of Zn/Mn ratio on the phosphate coating. To understand the process of phosphate coating formation, analysis of the surface morphology, element content, and structure of the resulting phosphate coating was performed under different phosphating times. The experimental results show that the zinc phosphate coating has a large plate-like structure and the manganese phosphate coating with a granular structure. The reflectivity of the phosphate coating is changed with the zinc-manganese ratio. The zinc phosphate coating has the highest reflectance, and the reflectance decreases with decreasing zinc-manganese ratio.The composite zinc phosphate coating is the most corrosion-resistant, and corrosion resistance decreases with decreasing zinc-manganese ratio. The grow rate of zinc phosphate coating formation was the fastest, followed by the composite phosphate coating, and the slowest was the manganese phosphate coating.