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.
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