The Microstructure And Properties Of Al-Mg₃Sb₂ Coating On Magnesium Alloy

With the development of automotive lightweight research,magnesium alloys are widely used in automotives because of their low density.At the same time,due their poor corrosion resistance,the further applications in automotives are restricted.In this paper,to improve the corrosion and wear resistance,expand the application range of magnesium alloy,the Al-Mg3Sb2 composite coatings were prepared on the surface of AZ31B magnesium alloy by thermal spraying.First of all,using the mechanical alloying to prepare Mg₃Sb₂ intermetallic compound powder,studying the mechanical and chemical behavior of Mg?s?+2Sb?s?=Mg₃Sb₂?s?reaction system in the process of mechanical alloying,ascertaining the optimum milling process under the present experimental condition is raw material ratio n?Mg?:n?Sb?=3:2,milling speed=500 r/min,ball ratio=15:1,sampling interval=2 h/time.Then,preparing the different composition of xAl-yMg₃Sb₂composite coatings by thermal spraying technology.The main phases in the coatings are Mg₃Sb₂ and Al.The microstructure of coatings are dense and less defects.Studying the basic properties of the coatings,such as hardness,electrochemical corrosion,dry friction and wear property by hardness tester,electrochemical workstation and high speed reciprocating friction tester.According to the actual conditions of magnesium alloy in the service process,the corrosion wear behavior of the coatings are also researched by improved high speed reciprocating friction tester.Moreover,the effects of the friction frequency on the corrosion wear resistance and dry friction and wear property of the coatings are studied by changing the frequency of friction.And the corrosion wear behavior of the coatings are further discussed.The results show that the intermetallic compound Mg₃Sb₂ can be obtained by mechanical alloying,and the reaction of 3Mg?s?+2Sb?s?=Mg₃Sb₂?s?is self-maintaining reaction.The micro-hardness of Al-Mg₃Sb₂ composite coatings increase with the increase of Mg₃Sb₂ content.The hardness of the coatings are all larger than that of the AZ31B magnesium alloy.The average micro-hardness of the?20%Al+80%Mg₃Sb₂?coating is 334.2 HV_0.025,which is 4.14 times higher than that of the AZ31B magnesium alloy.The electrochemical corrosion resistance of Al-Mg₃Sb₂ composite coatings increase with the increase of Mg3Sb2 content in 3.5%NaCl solution,and the corrosion resistance of the?20%Al+80%Mg₃Sb₂?coating is the best.Under dry friction condition,the friction and wear rate of Al-Mg₃Sb₂ composite coatings decrease with the increase of Mg₃Sb₂ content.The friction and wear rate of AZ31B is between 40%Mg₃Sb₂ and60%Mg₃Sb₂ coating,while the friction and wear rate of?20%Al+80%Mg₃Sb₂?coating decreases by 63.26%compared with that of AZ31B.In the corrosive wear test,the open circuit potential of AZ31B is always a straight line.The open circuit potential of the coatings with different components decrease after loading,and then rise after unloading.The open circuit potential of Al-Mg3Sb2 composite coatings are higher than that of AZ31B.During the loading period,the decrease range of the open circuit potential of the coatings decrease with the increase of Mg₃Sb₂ content.The open circuit potential of?20%Al+80%Mg3Sb2?coating is the highest and the corrosion tendency is the lowest.In addition,the wear rate of the coatings increase with the decrease of Mg₃Sb₂.The volume wear rate of?20%Al+80%Mg₃Sb₂?coating is 1.44 mm³?N^-1?m^-1,and 73.43%lower than that of AZ31B.In corrosive wear condition,the wear rate of the coatings are less than that of dry friction,but the wear rate of AZ31B is greater than that of dry friction.When change the friction frequency the wear rate of the coatings all increase with the increase of it in the two conditions,but the wear rate in the 3.5%Na Cl solution is smaller than under dry friction.The open circuit potential of the coatings decrease under the friction force,and the extend decrease with the increase of the friction frequency.The re-passivation ability of the coatings decrease with the increase of the friction frequency.