Study On Casting Method And Interface Behavior Of Continuous Carbon Fiber Reinforced Ductile Iron Crankshaft

Nodular cast iron crankshaft is a common part of automobile.Crankbearing is easy to fracture under high tensile stress.The traditional methods to improve the strength of nodular cast iron include alloying and heat treatment.However,because of the high cost of alloying and heat treatment,and the complex process,it is difficult to produce in large quantities,the research on strengthening of nodular cast iron has reached the ceiling.Carbon fiber is a kind of material with high strength,high modulus ratio,low density and low price.Adding carbon fiber into nodular cast iron to form new composites to obtain higher mechanical properties is a new strengthening idea.However,there is a problem of poor interface bonding between carbon fibers and iron base.Through surface modification of carbon fibers,carbon fibers were implanted into ductile iron by hand-made sand moulds.Tensile contrast tests were carried out on composite bars containing nickel-plated and non-nickel-plated carbon fibers by MTS Exceed E45electronic universal testing machine.The effect of nickel-plated layer on interface bonding was analyzed by QUANT FEG 250 electron microscopy and energy dispersive spectrometer.The test results show that:1.Nickel Electroplating on T700 Carbon FiberCarbon fiber heat treatment furnace de-gluing,temperature control at 400?,de-gluing time of 5 minutes,de-gluing more thorough.When HNO₃ is selected as coarsening solution,the temperature is controlled at 30?40? and the coarsening time is 80 minutes,the pit structure with moderate amount and size will be formed on the surface of the fibers,and the contact area with the nickel layer will be increased.The experimental conditions of nickel plating are pH 3-4.5,temperature25?,plating time 5 minutes,current density 0.5A/dm²,smooth and compact coating,thickness of 0.3?m is the ideal coating.2.Test method of hand-cast sand mold,tensile contrast test and analysis of carbon fiber oxidation resultsWhen making sand moulds,carbon fibers are embedded in both ends of sand box and tensioned,which can avoid uneven distribution of fibers caused by impact force produced by high density and high temperature hot metal casting.The tensile tests of nickel-plated and non-nickel-plated carbon fibers were carried out.The results show that the average tensile strength of nickel-plated carbon fiber bar is98 MPa higher than that of non-nickel-plated carbon fiber bar.At the same time,carbon fibers react with O to produce CO and CO₂ at 700?,which consumes C atoms in carbon fibers.Based on the analysis of carbon fiber oxidation reaction model,it is proposed that casting in inert gas or vacuum environment is an effective way to avoid carbon fiber oxidation.3.SEM and EDS Study on the Microstructure and Element Distribution of the Observed InterfaceThe effect of nickel layer on the interfacial morphology of carbon fiber reinforced iron matrix composites was observed by QUANT FEG 250 SEM.The nickel plated carbon fibers improved the interfacial bonding and wetted the carbon fibers and iron matrix.The concentration gradient of Ni atoms in the nickel layer was found by EDS surface scanning and EDS point scanning,and the diffusion of Ni atoms to the matrix was realized centered on carbon fibers.The metallurgical bonding of Fe-Ni-C interface was formed between carbon fibers and matrix with nickel layer as transition layer.