发动机缸体开裂失效分析

目的研究发动机缸体出现开裂失效原因。方法通过化学成分分析、力学性能分析、断口扫描分析、显微组织分析、能谱分析及低倍缺陷分析测试手段,对发动机缸体的开裂模式及失效原因进行分析。结果发动机缸体原材料中Si元素超标,导致晶界析出较多的Al Si Cu及Al2Cu脆性相,在开裂区域组织存在过热过烧现象,两个原因导致组织晶间结合力大大降低。同时,在开裂区域存在热节效应,低倍疏松和缩孔较集中的现象,为热裂纹形成及继续扩展提供了有利条件。结论通过不断改进设计工艺,控制原材料成分及调节浇注参数,大大减小了热裂纹出现概率,在后序批量生产中,未发现类似失效样件。

Failure Analysis of Fracture of Engine Cylinder Block

Objective To investigate reasons for fracture of engine cylinder block. Methods Fracture modes and the failure reasons were analyzed by chemical composition analysis, mechanical performance analysis, SEM analysis, microstructure, energy dispersive spectrum analysis and low magnification defect analysis. Results There were two reasons that greatly reduced the inter-granular binding force, one was caused by lots of brittle phases of Al2Cu and AlSiCu distributing along with the grain-interface which induced by excessive Si, and the other was superheating and over-firing microstructure in the cracking area. At the same time, there was hot section effect in the cracked area, and the low porosity and shrinkage cavity were concentrated, which provided favorable conditions for the formation and the continued expansion of hot crack. Conclusions The probability of hot cracking is greatly reduced by improving the process design, controlling raw material composition and adjusting casting parameters. There is no similar failure specimen in the post production.