V.S. Aigbodion

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.

Experimental Study of the Effect of Siliconizing Parameters of Thermochemical Treatment of low Carbon Steel

In order to use minimum time and save energy during siliconizing surface hardening of low carbon steel it is important to study the siliconizing parameters to obtain optimum conditions. In this work, the experimental design using the Taguchi method is employed to optimize the siliconizing parameters in the pack siliconizing surface hardening process. The siliconizing parameters evaluated are: siliconizing temperature, siliconizing time, silicon potential (ratio of silicon powder to bean pod ash (BPA) nanoparticle) and tempering temperature. The results showed that case depth and hardness values increased exponentially by increasing siliconizing temperature and time. Optimum values of hardness were obtained at a siliconizing temperature of 1000 ∘C, siliconizing time of 5 hours, silicon potential of 75 wt.% silicon/25 wt.% BPA and tempering temperature of 200 ∘C. With percentage contribution of: siliconizing temperature (79.86 %), siliconizing time (12.54 %), silicon potential (5.34 %) and tempering temperature (2.26 %). Silicon powder and bean pod ash nanoparticles can be effective for use as siliconizing materials in the ratio of 75 wt.% silicon/25 wt.% BPA. The activation energy (Q) for research work was determined as 333.89 kJ.mol−1. The growth rate constant (K) ranged from 6.78×10−8 to 2.05×10−6 m2.s−1. The case depth, hardness values and wear rate of siliconized mild steel at these operating conditions can be used for technological and industrial applications such as gears and cams.