Electrochemical studies and surface analyses of laser deposited Zn-Al-Sn coatings on AISI 1015 steel

Surface hardening of mild steel with Zn-Sn bath is characterised by the traditional phases, whereas presence of aluminium leads to coatings constituted by phase in the inner layers, and by an outer layer made of three phases and inter-metallic phases which made the materials to be brittle. Enhancement in properties of Zn-Al-Sn coating led to the investigation of Zn-Al-Sn coating on mild steel by laser alloying technique. Composition of 25%Zn-50%Al-25%Sn and 30%Zn-40%Al-20%Sn with laser power of 750 W, scanning speed of 0.6 and 0.8 m/min were used in this research. Standard techniques were used for the characterisation of the laser samples and 0.5 M H2SO4 was used for the electrochemical test. The results showed that all the properties were improved by increasing the Al content from 40 to 50%. The optimum properties were obtained at 25%Zn-50%Al-25%Sn at laser power of 750 W and speed of 0.8 m/min. The optimum composition significantly improved the corrosion resistance of Zn-Al-Sn coatings in 0.5 M H2SO4 solutions and 2.2-times the hardness of the substrate was also achieved. It has been established that laser alloying of mild steel with Zn-Al-Sn coatings is promising for improving the surface hardness values and corrosion resistance.