Distribution of α-AlFeSi and -AlFeSi particles in surface layer of AA6063 alloy billets after heat treatment

Abstract

We developed the EPMA mapping method of small α-AlFeSi(Al8.3Fe2Si) and β-AlFeSi(Al8.9Fe2Si2) particles in the billets of Al-Mg-Si alloys such as AA6063 alloys. To discriminate between α-AlFeSi and β-AlFeSi particles we used the relative X-ray intensities of Fe/Si ratio, the IFe/ISi ratio, instead of the Fe/Si mass ratio. To obtain the IFe/ISi ratio, we used a Monte Carlo method. In this study, using this method the mapping of α-AlFeSi and β-AlFeSi particles in the surface layer of AA6063 billets after the heat treatment (for 2 h at 580°C) was done. Namely, the distribution of α-AlFeSi and β-AlFeSi particles of zones from the billet surface to a depth of 800 μm was measured. Results showed the zone from the surface to a depth of 200 μm was occupied mainly by β-AlFeSi particles and the zone from a depth of 200 μm toward the center was occupied mainly by α-AlFeSi particles. From these results, it was found that if we remove zones from the surface to a depth of 200 μm, we can remove the majority of the β-AlFeSi particles, and thus improve the quality of anodizing performance of Al-Mg-Si alloys extrusions.