| By the micro-arc oxidation technology preparing the ceramic layer on the metal surface has the advantages of high temperature resistance,oxidation resistance,corrosion resistance,and tight bonding,and thus has received extensive attention in the field of surface treatment of magnesium and its alloys.However,due to the characteristic of the technology,the surface layer have a large amount of micro-pores and micro-cracks,which cause the mechanical properties and corrosion resistance to decrease,so how to solve the residual problem that the influence of pores on performance has become an important issue in the application of this technology.In response to this problem,the current researches include sealing agents,electroless plating,and sol-gel techniques.Among them,the surface treatment of the sealing agent is a technique that is simple in operation,low in cost,and wide in applicability.In the prior art,most of the technologies used organic sealing agents for surface treatment,but organic sealing agents had the disadvantages of poor heat resistance,high volatility,and non-environmental protection,so their applications were limited.Therefore,inorganic sealing agents with excellent thermal stability were used.Research has achieved rapid development.In this paper,the aluminum phosphate inorganic sealing agent with good thermal stability was prepared by hydrothermal synthesis reaction of phosphoric acid and aluminum hydroxide.With different sealing agent formulations,microarc oxidation of magnesium alloys was sealed under different sealing process parameters.Then XRD,TG-DSC,FT-IR,SEM,and Shore hardness analysis were used to study the sealants and sealing layer.The immersion corrosion test and the high temperature oxidation resistance test were performed on the sealing layer;Finally,the sealing mechanism of the magnesium alloy microarc oxidation ceramic layer with the aluminum phosphate inorganic sealing agent was analyzed and discussed.The results show that:1.The analysis of phosphoric acid and aluminum hydroxide with different ratios shows that when the molar ratio of aluminum hydroxide is excessive,the acidity of the sealing agent decreases,which in turn leads to a viscosity of the sealing agent decreases.The aluminum phosphate sealing agent can be synthesized at 50?-80?.The temperature increase will accelerate the reaction and shorten the reaction time.The aluminum phosphate sealing agent needs to be heat treatment at 400? when used to prevent deliquesce failure,the main phase of the sealing agent is a macromolecular aluminum phosphate ring;aluminum phosphate sealing agent is an excellent thermal stability inorganic sealing agent,used at high temperatures,weightlessness smaller.2.Through the experimental comparison found that the best sealing process:aluminum phosphate sealing agent P/A1 molar ratio of 3:1.2,viscosity of 240cp,the use of vacuum impregnation 5min,sealing treatment 2 times,and 400? heat treatment.When the sealing agent was added 6wt.%ZnO curing agent,the curing time decreased from 12h to 5h;the hardness increased from 80HA to 96HD.After soaking in 10 wt.%sodium chloride etching solution,the weight loss of the sample after sealing is about 54%lower than that of the unsealed sample.In the high temperature oxidation test,the weight loss of the sample after sealing is compared to the unsealed.The hole-treated sample was reduced by about 72%.3.The conclusion that aluminum phosphate inorganic sealing agent seals the magnesium arc micro-arc oxidation ceramic layer is due to physical adsorption forms van der waals forces between the aluminum phosphate sealing agent and the micro-arc oxidation ceramic layer and the aluminum phosphate sealing agent and the micro-arc oxidation ceramic layer chemical reactions occur between the aluminum magnesium phosphate to produce chemically bonded pores. |
PDF Full Text Request