Effect Of A Small Amount Of Se On The Formation Of Anti-oxidation Protective Film On The Surface Of Low Alloyed Cu-Si Alloy Under Preheating Treatment

Copper（Cu）is widely used in numerous industrial fields because of its excellent electrical and thermal conductivity.However,Cu is easily oxidized at high temperature,which greatly limits its application.So far,people have used different methods to prevent the oxidation of Cu.Among them,alloying process has attracted extensive attention due to its advantages of simple operation and environmental protection.The results show that adding a small amount of Sior Se to Cu can improve its high temperature antioxidant capacity.The oxidation resistance of Cu-Siand Cu-Se binary alloys can be further improved by preheating them in hydrogen atmosphere.The improvement of the oxidation resistance of Cu-Sialloy can be attributed to the formation of the protective film on the surface of the heat-treated alloy in hydrogen atmosphere.However,due to the high requirement of the forming temperature and time of the protective film.That is,the temperature should be 800°C,the holding time should be at least 24 h,and the cooling rate is 0.5°C/min,which cost large energy consumption.The oxidation resistance of Cu-Se alloy is improved because the Cu₂Se segregation layer formed on the surface of the alloy cannot react with oxygen to produce copper oxide,but the protection of the segregation layer is limited,and it still cannot inhibit the high-temperature oxidation for a long time.Therefore,it is necessary to prepare new copper alloys to reduce the cost of preheating treatment on the premise of ensuring the oxidation resistance of copper.On the basis of the above studies on the oxidation resistance of binary copper alloy,this paper mainly studied the preparation of ternary Cu-Si-Se alloys（x=0.5,1.0 wt.%,y=0.2,0.5 wt.%）by adding a small amount of alloying element Se to the low alloyed Cu-Sialloys,and improved their high temperature oxidation resistance by preheating treatment.And how to reduce the preheating temperature,shorten the holding time and increase the cooling rate by optimizing the preheating conditions under the premise of guaranteeing the antioxidant capacity.The influence of different preheating conditions（T_p=400-800°C,t=6-24 h and r_c=0.5-5°C/min）on the formation of surface protective layer of Cu-Si-Se alloys was firstly studied in this thesis.It is found that,high quality and dense SiO₂ protective film can be formed on the surface of the alloys when the temperature is 600°C,holding for24 h and cooling rate is 2°C/min,or 800°C holding for 12 h and cooling rate is2°C/min.Therefore,compared with binary Cu-Sialloys,the preheating conditions of Cu-Si-Se alloys have been much improved with reduced temperature and holding time and increased cooling rate.During the preheating process,the formation of the surface protective film is related to the segregation and diffusion of Siand Se.Siforms a protective layer of SiO₂ while Se also forms a segregation layer of Cu₂Se on the surface of the alloys by diffusion.Compared with Cu-Sibinary alloys,the decrease of preheating temperature required by Cu-Si-Se ternary alloys to form SiO₂ protective film is related to the addition of Se,because the lattice distortion caused by Se is conducive to the diffusion of Si.In terms of the influence of cooling rate,if the cooling rate is too low,the energy consumption will increase,while excessive cooling rate will damage the protective film due to the large expansion coefficient difference between the alloy matrix and the surface protective film.On the basis of the above work about preheating,the oxidation resistance of the preheated Cu-Si-Se alloys was tested in air at 400°C.The Cu-Si-Se alloys obtained at600°C holding for 24 h and at 800°C holding for 12 h all showed excellent oxidation resistance,which was corresponding to the surface protective film characterization results of the alloys preheated.The excellent oxidation resistance of Cu-Si-Se alloys is mainly due to the formation of complete and dense SiO₂ film on the surface,and the formation of Cu₂Se segregation layer near the surface also plays an auxiliary role in improving the oxidation resistance of the alloys.The results show that,compared with Cu-Sibinary alloys,adding a small amount of Se element in Cu-Sialloys can completely reduce the preheating temperature and holding time,thus reducing the energy consumption.Relative to the rapid cooling（5°C/min）case,in addition,when the rate was increased from 0.5°C/min to 2°C/min,the oxidation resistance of Cu-Si-Se alloys was not weakened,which was also conducive to the reduction of energy consumption during the preheating process.