热浸镀铝球墨铸铁失效机理研究

Failure Mechanism of Hot Dip Aluminized Ductile Iron

采用VK-9710型激光共聚焦显微镜对热浸镀铝球墨铸铁试样的三点弯曲失效过程进行原位观察,分析镀层和基体的裂纹萌生和扩展机理。结果表明:对于纯Al浸镀球墨铸铁,在拉应力作用下,铁铝合金镀层率先萌生裂纹,诱导临近基体中铁素体撕裂与石墨球剥离,裂纹近似垂直于拉应力方向并沿着临近石墨球最短途径扩展;压应力导致表面纯Al层剥离和铁铝合金层破碎,镀层失效对球墨铸铁基体基本无影响。对于Al-3.7Si-1.0RE浸镀球墨铸铁,拉应力作用下的失效机理与纯Al浸镀相似;压应力作用下纯Al层和铁铝合金层与基体脱开,表现为铁素体基体失效。

Using laser scanning confocal microscope,failure process of aluminized ductile iron samples were in-situ observed during three-point bending test,while crack initiation and propagation mechanism were analyzed in the area of coating and matrix.The results show that for hot-dipped samples in Al,cracks mainly initiate in the Fe-Al alloy coating under tensile stress,then induce the tearing of ferrite and the peeling of graphite in the adjacent matrix.Thereby cracks spread to the inner matrix in shortest route between graphite and ferrite,in the direction nearly vertical to tensile stress.In case of compression stress,aluminized alloy layer is crushed and aluminum layer is peeled off,which having little influence on the failure of matrix.For hot-dipped samples in Al-3.7Si-1.0RE,failure mechanism under tensile stress is similar to that of hot-dipped samples in Al;under compression stress,aluminum and Fe-Al alloy coatings are disengaged from matrix,exhibits failure occurring in the ferrite matrix.