摘要
车用R14铝合金拔叉铸件在使用过程中发生断裂。利用光电直读光谱仪、金相显微镜、扫描电子显微镜对发生断裂的压铸件的化学成分、组织、断口形貌和微区成分进行分析。结果表明:倒档拔叉R14铝合金材料化学成分、力学性能和表面硬度均合格,但其近表层的针孔度及截面突变处的R角均不符合设计要求;截面突变处存在的疏松缺陷及较大的应力集中使失效件承受拉应力时裂纹在疏松处萌生,在往复的拉压应力下裂纹快速扩展并最终导致断裂的发生;建议在拔叉铸件压铸成型后增加针孔度检查及增加截面突变处R值。
Fracture occurred to a R14 aluminum aioy shifting fork casting in the truck during service. Chemical composition,microstructure,fracture morphology and microarea composition anlysis of the fractured shifting fork casting were analyzed by means of photoelectric direct reading spectrometer, metallographic microscopy, SEM and SDD EDS to investigate the fracture cause. The analysis results indicate that the chemical composition,mechanical properties and hadness of the fractured shifting forkcasting were all qualified. However,the nearsurfacc pinhole grade and Rangle of abrupt change area of the cross-section did notmeet the design requirement. Due to porosity defects at the abrupt change area of the cross-section and stress concentration,cracksinitiated from the porosity defects while the failed part bore tensile stress and propagatedwhich led to the final fracture. To avoid such failure, some measures were proposed and applied, such as performing pinhole testingafter shifting fork casting’s compression molding and increasing Rangle of abrupt change area of the cross-section.
出处
《失效分析与预防》
2016年第3期176-181,共6页
Failure Analysis and Prevention
关键词
R14铝合金
拔叉
开裂
失效分析
疏松
针孔
R14 aluminum alloy
shifting fork
fracture
failure analysis
porosity
pinhole
