Preparation And Characterization Of Phosphate Coating On TC4 Alloy Surface

Aluminum dihydrogen phosphate has the characteristics of good adhesion,heat resistance,antioxidant,non-toxic and non-polluting,and can be used as adhesive material for coating adhesives.However,when aluminum dihydrogen phosphate is used as adhesive material for coating adhesives,There are still some problems:aluminum dihydrogen phosphate bond material can not be widely used in life because its curing temperature is too high.Therefore,the purpose of this paper is to study the modified curing agent to reduce the curing temperature of coating adhesive.At the same time,the influence of curing agent,bonding material and filler?aluminum powder?on the coating morphology,curing time and hardness were investigated.In this experiment,aluminum hydroxide and phosphoric acid were used as raw materials to prepare aluminum dihydrogen phosphate bonding materials.The selected molar ratios of phosphoric acid and aluminum hydroxide are 3:1.0,3:1.2,3:1.4,3:1.6in the experiment,respectively.The prepared aluminum dihydrogen phosphate bonds were characterized by XRD.The results showed that when the ratio of phosphoric acid to aluminum hydroxide moles was P/Al=3:1.4,The reaction product is mainly aluminum dihydrogen phosphate.At the same time,aluminum oxide was prepared by using aluminum isopropoxide,which were coated on the surface of MgO,ZnO,MgO whisker and ZnO whisker to prepare modified curing agent?MgO@Al₂O₃,ZnO@Al₂O₃,MgOw@Al₂O₃,ZnOw@Al₂O₃?.the composition and morphology of modified curing agent particles were characterized by XRD,SEM-EDX and TEM.The results showed that Al₂O₃ successfully covered the surface of MgO,ZnO,MgO whiskers and ZnO whiskers.The coatings were prepared by using the four modified curing agents and the aluminum dihydrogen phosphate binding materials and applied to the surface of TC4alloy.In the experiment,the quality ratios of modified curing agent and aluminum dihydrogen phosphate bonded material were 10:0.5,10:1.0,10:2.0,respectively.In order to investigate the influence of aluminum powder on surface morphology,curing time and hardness of coating,SEM characterization was carried out,and curing time and hardness of coating were determined.The results showed when the quality ratio of the aluminum dihydrogen phosphate adhesive and the modified curing agent is10:1,the curing time are 120 min,150 min,80 min,and 90 min,respectively.The surface of the coating was flat and no cracks.The hardness values reached 90.6 HRB,90.3 HRB,91.1 HRB,91.5 HRB,respectively.At the same time,it was found that the effect of using the modified curing agent MgOw@Al₂O₃ and ZnOw@Al₂O₃ to cure the aluminum dihydrogen phosphate binder is better than that of the modified curing agent MgO@Al₂O₃ and ZnO@Al₂O₃.In the following study,the modified curing agent?MgOw@Al₂O₃ and ZnOw@Al₂O₃?were used as curing agents,and the mass ratio of the added aluminum dihydrogen phosphate bonding material and the modified curing agent was 10:1.Different amounts of aluminum powder were added respectively,so that the mass ratio of the bonding substance,the curing agent and the aluminum powder in the coating were 10:1:0,10:1:0.05,10:1:0.1,10:1:0.2,respectively.The coating was characterized by SEM,and the curing time and hardness of the coating were tested,and the effects of aluminum powder addition on the curing time,surface morphology and hardness of the coating were investigated.The results of the investigation showed that when MgOw@Al₂O₃ was used as curing agent,the curing time was 60 min,50min,40 min,and 30 min after adding different proportions of aluminum powder,and the hardness was 91.1 HRB,96.5 HRB,85.3 HRB,80.9 HRB,respectively;When ZnOw@Al₂O₃ was used as curing agent,the curing time was 70 min,50 min,45 min,and 40 min,respectively,and the hardness was 91.5 HRB,93.1 HRB,80.2 HRB,and62.2 HRB.The experiment shows that with the addition of aluminum powder,the curing time of the coating is shortened,but the hardness value of the coating is first increased and then reduced.The reason may be that the surface of the coating has a lamellar structure with the addition of aluminum powder,and the surface is more prone to cracks.Finally,the coating of the bonding material,curing agent and aluminum powder with a mass ratio of 10:1:0.05 was subjected to high temperature oxidation experiments of 800°C and 5 hours.The hardness of the coating before and after oxidation was compared and the surface morphology of the coating was observed by scanning electron microscope.The results showed that when MgOw@Al₂O₃ is used as the curing agent,the hardness of the coating increases from96.5 HRB to 99.2 HRB after high temperature oxidation;when ZnOw@Al₂O₃ is used as the curing agent,the hardness of the coating increases from 93.1 HRB to 98.2 HRB after high temperature oxidation.Through scanning electron microscope observation,it is found that the surface of the coating sample is flat and crack free,the connection between grain and grain is closer,the lamellar structure disappears,and the surface becomes granular dispersion.According to the surface morphology and hardness of the coating before and after oxidation,the prepared coating has good high temperature resistance.According to the experiment,when MgOw@Al₂O₃ and ZnOw@Al₂O₃ are used as curing agents,the curing temperature of the aluminum dihydrogen phosphate bond material can be reduced and the curing time extended.After adding aluminum powder,the reaction rate of curing agent and bonding material can be accelerated.At the same time,the coating prepared has good temperature resistance.