Laser Alloying of an Al-Sn Binary Alloy onto Mild Steel: In Situ Formation, Hardness and Anti-Corrosion Properties
O.S. Fatoba, A.P.I. Popoola and V.S. Aigbodion
Surface hardening of mild steel with Al-Sn is characterized by the traditional phases, whereas the presence of Al leads to coatings constituted by phase in the inner layers and by an outer layer made of three phases and intermetallic phases which cause the materials to become brittle. In order to enhance the properties of Al-Sn coatings on mild steel, the investigation of Al-Sn coating on mild steel by the laser alloying method using a Nd:YAG laser was carried out. A laser power of 1100 W, scanning speeds of 0.6 and 0.8 m/min, and alloy compositions of 25Al- 75Sn, 50Al-50Sn and 75Al-25Sn were used in the research. The mild steel alloyed surfaces were examined in terms of hardness and corrosion behaviour at different laser processing conditions. The results showed improved properties by increasing the Al content from 25 to 75%. The optimum properties were obtained at 75Al-25Sn alloy at laser power of 1100 W and speed of 0.8 m/min. The corrosion rate at optimum composition gave significant protection in 0.5M H2SO4 solution and double the hardness of the substrate was achieved. At scanning speed of 0.8 m/min, the highest polarization resistance, Rp, of 3245500 Ωcm2, the lowest corrosion current density, Icorr, of 1.82 × 10-8 A/cm2 and lowest corrosion rate, Cr, of 0.00021 mm/year in 0.5M H2SO4 solution. It was established that laser alloying of mild steel with of Al-Sn is promising for improving the surface hardness values and corrosion resistance for engineering applications.
Keywords: Nd:YAG laser, mild steel, Al-Sn binary alloy, coating, hardness, corrosion rate, polarization resistance