Analysis of a diesel engine cylinder head failure caused by casting porosity defects

The diesel engine failed in the bench test due to the cracking of its cylinder head, which is made of aluminum alloy by low pressure sand casting. To investigate the cause of the cylinder head cracks, computed tomography (CT), metallurgical observation and fracture inspection were carried out. Besides, the stress state of the cylinder head was determined by finite element analysis method, and the casting process was simulated to identify the root cause of the cracks. The cracks are observed to be mainly concentrated at the intake/exhaust channel and the cooling water channel, especially at the partition wall between them. At the partition wall, the cracks mostly initiate from the outside wall and propagate to the interior surface, some of which have penetrated the partition wall. The cylinder head failure is promoted by multiple cracks initiated in casting porosity defects, independent of the loading condition, as proved by the results of finite element method and crack morphology. Furthermore, the formation of casting porosity defects in the cylinder head is caused by poor local cooling conditions during the casting process.