Microstructure and corrosion resistance of an Al-bronze coating prepared by cold metal transfer on 27SiMn steel

By using the cold metal transfer welding technique, an S215 Al-bronze repair layer (-850 um in thickness) was successfully fabricated on the surface of 27SiMn steel. The microstructure of the repair layer was characterized by X-ray diffraction, electron channeling contrast imaging, energy dispersive spectrometry and electron backscatter diffraction techniques. Corrosion resistance and hardness of the repair layer were evaluated using an electrochemical workstation and a Vickers hardness tester, respectively. The repair layer mainly consists of near equiaxed Cu-phase grains and dispersed alpha-Fe particles (with interlaced fine laths as internal substructures) resulting from the liquid phase separation of the Cu-Fe system during rapid solidification. The corrosion resistance of the repair layer (Ecorr: -463.2 mV and Icorr: 1.263 uA/cm2) is found substantially superior to that of the substrate (Ecorr:- 658.9 mV and Icorr: 3.310 uA/cm2). The corrosion rate of the repair layer is reduced by -59.2 % compared to the substrate. This improvement is related to the formation of protective passive films (Cu/ Al-oxides) on the repair layer during electrochemical corrosion. This research should be able to provide valuable insights for preparing corrosion-resistant repair layers for steels.