Samples of the cross section microstructures of galvannealed steel sheets that lack alloying were analyzed.X-ray diffraction(XRD) tests were carried out.The study discovers that the deficit of alloying was higher on both sides of the steel sheet when compared to the center and the thickness of the coating on the sides was also higher than the center.The results of the XRD tests demonstrate that the microstructure of the coating with a lack of alloy is mainly composed of zinc,ζ and δ.They also indicate that the lack of alloying is mainly due to a lower galvannealing temperature and thicker coating.It is shown by the optical micrographs of coating that the δ phase forms first in a discontinuous manner at the interface and then rapidly pushes towards the coating and enlarges.
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