Profile of implanted nitrogen ions in Al alloy for mold materials

Nitrogen ions were implanted into an aluminum alloy (Al-7Si) for casting mold materials by plasma-based ion implantation to enhance wear resistance and hardness of the target. A negative high-voltage pulse of 10 kV with a pulse width of 10 μs and repetition rate of 100 Hz was applied to the target immersed in the nitrogen plasma produced by filament discharge. Auger electron spectroscopy (AES) analysis indicated that the depth profile of implanted nitrogen had two peaks, corresponding to N+ and N2+ ions, for short implantation times less than approximately 30 min. For implantation times longer than 30 min, however, the two peaks merged with each other. The AES analysis also indicated the formation of AlN by implantation of nitrogen ions. The AlN was formed in the surface region within the nitrogen ion range. A wear-resistance test by the ball-on-disc method showed that nitrogen ion implantation resulted in a reduction of the friction coefficient from 0.6 to 0.1 and the wear resistance was increased by one order of magnitude. It was also found that nitrogen ion implantation enhances the hydrophilic properties.