Analysis of Solidification Behavior of Compacted Graphite Iron Exhaust Manifold and Its Comparison with Si-Mo Ductile Iron

With high peak pressure demands and the need for improved engine efficiency, it has become necessary to use lighter and stronger materials for different engine components. Compacted Graphite Iron (CGI) in this area is a promising candidate and is currently used for many casting parts like cylinder block, head, cylinder liner, exhaust manifold, engine frame, etc. The internal quality of these components made from CG iron is crucial for improved engine performance. The internal quality, in turn, depends upon the soundness and solidification behavior of casting components. However, there exist very limited data on the solidification behavior of CG iron for different engine castings. Due to the narrow range of microstructure stability, CG iron production and its solidification is a quite challenging process. In this paper, a study is undertaken for one such engine component exhaust manifold made from CG iron. An in-depth analysis is carried out on exhaust manifold casting to understand its solidification behavior using a casting simulation software MAGMA. Using the simulation, phenomena associated with fluid flow, temperature distribution, mushy zone formation, hot spot, and shrinkage were examined. Microstructure predictions like nodularity were also studied. Prediction of residual stresses and strains in the casting upon solidification were understood for CG iron through simulation. Finally, a comparison was made with all the above solidification parameters of CG iron with another widely used Si-Mo ductile iron material for the exhaust manifold. CG iron showed improved fluidity, higher heat loss, lesser area of hot spot, and lesser porosity formation tendencies compared to Si-Mo ductile iron. It showed a higher amount of residual stresses than Si-Mo due to differences in thermal conductivity and thermal expansion coefficients. Tendencies for warpage and dimensional stability were also compared and found to be better with CG iron than Si-Mo ductile iron