Influence of Pre-Tinning Process on Coating Morphology and Interface Structure of Low Carbon Steel Dipped in Molten 6061 Al Alloy

Abstract

Pre-treated low carbon steel specimens with flux or flux + tin mixture were coated by hot-dip aluminizing process. Al alloy (6061) was melted and hold at 750 °C. Fluxed and pre-tinned low carbon steel samples were dipped in a molten bath for time intervals of 0.5, 1, 2.5 and 3.5 min. Applying double coating processes via tinning-aluminizing techniques facilitated the formation of Fe-Al intermetallic interface and increasing the thickness of homogenous coating layer over the substrate material. The presence of Sn facilitates to great extent the formation of a better interlayer-free bond of residual flux and/or oxides. The fluxed–dipped steel substrates have inhomogeneous distribution of Al alloy coating as well as an interface with residual flux and oxides for dipping time up to 2.5 min. A homogenous distribution with good thickness morphology of the Al alloy coating and homogeneous thin intermetallic interface was achieved for tinned steel substrate at all applied dipping times. The comparison between the pre-tinning and pre-fluxing processes on steel substrates showed a significant effect of tinning over fluxing treatment acting on the thickness layer of Al-coating and interface using a short time dipping. For dipping time up to 2.5 min, the hardness of pre-tinning substrates is greater than that of fluxed ones due to the presence of residual flux and void interface in fluxed steel.