汽车发动机气缸盖开裂原因分析

Fracture causes analysis of cylinder head on automotive engine

针对气缸盖耐久试验时过早出现漏水问题展开失效分析。首先通过宏观检查发现裂纹源来自内表面,裂纹源沿清砂孔外圆凹槽内产生,沿凹槽向两端断续延伸,同时从冷却腔体内沿壁厚方向外伸。裂纹是在凹槽内多处多次产生并扩展,呈热裂纹特征。用显微检查、化学成分分析、硬度检验等常规失效分析手段,进一步确认气缸盖开裂原因是热疲劳,而铸造应力、机械应力对开裂和裂纹扩展也有间接作用。

Failure analysis was directed against water＇s leaking untimely through cylinder head during an engine＇s durability test. At first, it was found that crack source came from inner surface by macroscopic view checking. Crack source grown just along indentation around outer-circle of the sand cleaning hole, extending interrupted along indentation, in the meantime penetrating the wall from the cooling chamber. Cracks appeared many times in many location with thermal cracks characteristic. It was further confirmed that fracture causes of cylinder head was thermal fatigue by normal failure analysis method such as visual inspection, microscope check,element analysis and hardness test.While casting and mechanical stress played indirect action.