Microstructure and Performance of Al-Coating on AZ31 Prepared by Pack-Cementation with Different Heating Methods

In this study, Al-containing coatings were prepared on the surface of AZ31 magnesium alloy by pack-cementation through box-type furnace heating (BFH) and induction heating (IH) methods. Phases, microstructure, composition, and performance were characterized by X-ray diffraction technique (XRD), secondary electron imaging (SEI), backscattered electron imaging (BSEI), and energy dispersive spectroscopy (EDS), the Vickers hardness test and potentiodynamic polarisation test, respectively. The results show that the heating method has a significant impact on the phases, microstructure, thickness, and performance of the coatings. Both aluminized layers are relatively flat and dense, and no obvious second phase is observed. The thickness of the aluminized layer of the IH sample is much larger than that of the BFH sample because the diffusion rate of IH is greater than that of BFH. Both aluminized layers are composed of an outermost layer of β-Mg2Al3 and an inner layer of γ-Mg17Al12 near the side of the substrate. The evolution of different heating methods is discussed. The microhardness and corrosion behavior of the aluminized coatings were also investigated and discussed. The results indicate that the hardness and corrosion resistance of the IH diffusion sample is better than that of the BFH, and this is related to the content of the intermetallic compound phase.