Study On Technique Of Copper Aluminizing And Its Surface Properties

Copper and its alloys are important metal material in both traditional and modernsociety. Copper alloy not only has beautiful appearance, but it’s also excellent inthermal conductivity properties and processing performance, which makes it widelyused in modern industry. Copper alloy parts have high cost, wear and corrosion is themain reason for the failure during our practical production of life, therefore, surfacetreatment is an effective method to prolonging the service life of copper alloy partsand decreasing its cost of using. There are many ways in the surface modification ofcopper alloy, for example, the infiltration casting method, the inner surface oxidation,the thermal spray technology and the plasma nitriding titanium technology. Thisarticle will adopt solid powder aluminizing technique, discuss aluminizing mechanismand put forward reasonable production process blue print to improve the surfaceproperty of the copper alloy material including wear resistance, hardness andcorrosion resistance.Copper surface aluminizing is alloying process base on the elemental diffusionand a series of chemical reactions. Resistance-type crucible furnace and cruciblesealed by clay is the necessary equipment of aluminizing, powder infiltration agentincluding pure aluminum, alumina powder (mainly for filling) and ammoniumchloride (catalysis). By orthogonal experiments and study on the macro morphologyof specimen, preliminary test scheme is confirmed. Using scanning electronmicroscope (SEM) and X-ray Diffraction (XRD), make sure that the content ofaluminum will affect the phase composition of aluminized layer, the aluminized layercontain α-Cu, phase and Al2O3which can improve the comprehensive performanceof the material. The alloying layer from inside to outside is: copper substrate-Cu (+)or+(+γ1)(with Al2O3) surface deposited aluminum.According to the macro and micro morphology, the optimum process conditions ofaluminizing is confirmed, which is the heating temperature is800℃~900℃andholding2~3hours, the content of aluminum powder is40%, the content of aluminumpowder is40%and catalyst content is at least2%in the infiltration agent. Thealuminized layer thickness is about1mm with homogeneous microstructure and thesintered layer is flimsy without any surface burning.Through the test and analysis of abrasive wear about aluminizing copper andpure copper, the wear quality of aluminizing copper is only1/21/3of the pure copperin the same wear condition, the wear resistance of aluminizing copper is better thanthat of pure copper is more significant in the high load and high coefficient of frictioncondition. When the content of aluminum powder is40%45%in the infiltrationagent, the aluminizing copper has the best wear resistance performance. Through thetest of micro hardness about aluminizing copper, the micro hardness of aluminizedlayer is about110HV and two times as large as the copper substrate. From thesubstrate to the surface the micro hardness has increasing trend, the hardness ofsintered layer is up to190HV.Through the test of electrochemical corrosion about aluminizing copper by thethree electrode system, and analysis the polarization curve base on Tafel theory, it canbe obtained that800℃-2.5h-2%-40%aluminizing copper has the best corrosionresistance performance, the corrosion potential reaches-0.34V, higher than that ofpure copper about-0.57V,the corrosion current density is5.62A cm-2, lower thanthat of the other two kind of aluminizing copper about6.92A cm-2and7.41A cm-2.Therefore, the corrosion resistance of aluminizing copper was improvedto some extent compared with the pure copper.