Study On Microstructure Characteristics Of Ductile Iron Alloy Via Lost Foam Casting By Vibration Solidification

In recent years, the lost foam casting (LFC) process of ductile iron is developingrapidly because it has many advantages such as precision forming, clean production, andso on. The LFC is widely used in mass production, especially for small castings. Becausedry sand is used in LFC, the cooling rate of casting is relatively slow, and the eutectictransformation of ductile iron suffers a long duration. For this reason, the graphite numberdecreases and the graphite morphology becomes bad, and the mechanical properties ofcastings descend. In this study, the vibration method was used to refine the graphite andmicrostructure to solve the problem of insufficient mechanical properties of ductile ironcasting produced by LFC.The effects of vibration frequency and casting thickness on graphite morphology,microstructure and hardness of the ductile iron obtained by LFC were studied, and thecasting defects in the experiment were also investigated. Based on Image J software, anew method was developed to analyze the microstructure of ductile iron.(1) It had been researched that the effects of vibration frequency on graphitemorphology, microstructure and the hardness of ductile iron via LFC. The results showedthat the number of graphite increased but the proportion of coarse graphite and theproportion of carbide in thin-walled ductile iron decreased with increasing vibrationfrequency.(2) It had been researched that the effects of casting thickness on graphitemorphology, microstructure and the hardness of ductile iron via LFC. The results showedthat the number of graphite, the hardness and the roundness decreased while theproportion of coarse graphite increased with the increase of casting thickness in staticsolidification condition. The number of graphite increased, but the proportion of coarsegraphite and the roundness of graphite had no significant changes, and the hardnessdecreased with the increase of casting thickness in vibration solidification. Therefore, thegraphite morphology was uniformed for different casting thicknesses through the vibration.(3) The white iron casting defect in the experiment was firstly investigated.Meanwhile, the effects of vibration on white iron via LFC were also studied. The resultsshowed that the pearlite was more uniformed and the proportion of pearlite increased invibration solidification condition. Some of the secondary dendrite was broken, and themetamorphosis ledeburite in the matrix microstructure was fined and uniformlydistributed.(4) Based on Image J software, a new method was developed to analyze themicrostructure of ductile iron. The number of graphite, area, percentage, roundness,orientation angle, and nodularity can be calculated, as well as the pearlite, carbide andferrite in the matrix. This method is simple and easy to popularize, which effectivelyimproves the accuracy and the efficiency of the measurement.