Casting defects and microstructure distribution characteristics of aluminum alloy cylinder head with complex structure

Abstract

Due to the complex structure of the large cylinder head, it is prone to produce uncontrolled casting defects and uneven microstructure distribution. In order to predict the porosity defects and secondary dendrite arm spacing (SDAS) in the as-cast cylinder head, the low pressure casting process of aluminum alloy cylinder head was simulated. Moreover, to verify the accuracy of the simulation results, microscopic observations were performed, in which the simulation results are reasonably matching with that of experiment results. Both simulation and experiment results demonstrate that porosity defects mainly exist in thick walls as well as thick-thin wall junctions. In addition, the top plate presents the finest microstructure, while the microstructure of the force wall is the coarsest. Additionally, the correlation of casting parameters with porosity defects and microstructure was discussed, suggesting that increasing the cooling rate could partially reduce porosity defects. Furthermore, the finding that decreasing the cooling rate can reduce the SDAS of the casting, resulting in a dense microstructure, was drawn. Besides, it has been concluded that regular shapes and thin walls are advantageous for both reducing porosity defects and obtaining uniform microstructures. This provides an effective approach for predicting the casting defects and microstructure of large complex structural castings through numerical simulation. In addition, a quantitative understanding of the casting parameters, complex structure-microstructure relationship for cast aluminum alloys will allow better determination of process parameters based on microstructure and properties requirements of complex components.