Study On Process,Microstructure And Properties Of Hot Dipping And Diffusion Aluminizing On Cast Iron

Due to its excellent properties,cast iron is widely used in valve guide,crank train and cylinder block of automobile engine.Owing to its special word environment,it is often invalidated by oxidation and wear.In order to improve the high temperature oxidation resistance and wear resistance of cast iron,Fe-Al alloy layer was prepared on the surface of cast iron by hot dipping and diffusion aluminizing(HDDA).The effects of technological parameters and graphite morphology on the microstructure and properties of HDDA layer of spheroidal graphite cast iron(FCD)were studied.The results show that the optimum technology of HDDA as follow:aluminizing temperature at 730?,aluminizing time for 5 min,diffusion temperature at 900?and diffusion time for 4 h.Under the best technology,a dense and uniform needle-like Al₂O₃film is formed on the surface of HDDA layer.The outer layer is Fe₂Al₅phase,the inner layer is Fe Al phase,and the graphite in the matrix is not oxidized.With the increase of diffusion temperature(700-1000?),the high temperature oxidation and wear resistance of HDDA FCD increase gradually.With the extension of diffusion time(1-5h),the high temperature oxidation and wear resistance of HDDA FCD increase first and then decrease.When diffusion time is 4 h,the high temperature oxidation resistance and wear resistance of HDDA FCD reach the best value.After 72 h of oxidation at 750?,the weight increment per unit area of FCD is 30.4532 mg/cm²,while HDDA FCD is 1.5357 mg/cm²under the optimum process,which is only 1/20 of FCD.After 20 min wear test,the friction coefficient of FCD is about 0.07 and the abrasion loss is 0.3613 mm³,while HDDA FCD is about 0.35 and 0.2732 mm³under the optimum process.Therefore,HDDA can reduce the attrition resistance and improves the wear resistance.Graphite morphology does not affect the phase composition of HDDA layer,but affects the morphology and properties of HDDA layer.There are holes in the HDDA layer of flake graphite cast iron(FC),while the HDDA layer of FCD is uniform and dense.HDDA FCD is superior to HDDA FC in high temperature oxidation resistance and wear resistance.