Laser surface aluminizing of mild steel : microstructural and corrosion characteristics

摘要

Laser surface alloying of mild steel AISI 1050 using aluminum alloy (AlFeSi) wasrnattempted. Alloying material in powder form was preplaced on the surface of the substraternby oxyfuel flame spraying. The surface was then consolidated by scanning with a 2-kWrnCW Nd:YAG laser beam. The microstructures of the alloyed layers were studied byrnscanning electron microscopy, optical microscopy and X-ray diffractometry. The corrosionrnand cavitation-erosion characteristics in 3.5% NaCl solution at 23 ℃ were studied byrnpotentiodynamic polarization technique and by means of a 20 kHz ultrasonic vibratoryrnfacility. The laser-alloyed specimens were found to be composed of ferrite and thernintermetallic phases Fe_3Al, FeAl and Fe_2Al_5. The maximum hardness was significantlyrnincreased to 595 Hv. The corrosion behaviour was influenced by the degree of dilution ofrnthe alloying element. Although aluminizing led to an active shift in the corrosion potentialrnfrom -510 mV to -890 mV, the specimens showed passivity with pitting and protectionrnpotentials of –550 mV and -710 mV respectively while the substrate did not. The corrosionrnresistance of the laser-alloyed specimens was significantly improved as evidenced by arnmuch lower corrosion current density. In addition, the cavitation-erosion resistance of thernlaser-alloyed specimens was also significantly improved by 17.7 times that of the substraterndue to the increase in both hardness and corrosion resistance of the laser-alloyed layer.