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

We developed the EPMA mapping method of small alpha-AlFeSi(Al8.3Fe2Si) and beta-AlFeSi(Al8.9Fe2Si2) particles in the billets of Al-Mg-Si alloys such as AA6063 alloys. To discriminate between alpha-AlFeSi and beta-AlFeSi particles we used the relative X-ray intensities of Fe/Si ratio, the I-Fe/I-Si ratio, instead of the Fe/Si mass ratio. To obtain the I-Fe/I-Si ratio, we used a Monte Carlo method. In this study, using this method the mapping of alpha-AlFeSi and beta-AlFeSi particles in the surface layer of AA6063 billets after the heat treatment (for 2 h at 580degreesC) was done. Namely, the distribution of alpha-AlFeSi and beta-AlFeSi particles of zones from the billet surface to a depth of 800 mum was measured. Results showed the zone from the surface to a depth of 200 mum was occupied mainly by beta-AlFeSi particles and the zone from a depth of 200 mum toward the center was occupied mainly by alpha-AlFeSi particles. From these results, it was found that if we remove zones from the surface to a depth of 200 mum, we can remove the majority of the beta-AlFeSi particles, and thus improve the quality of anodizing performance of Al-Mg-Si alloys extrusions. (C) 2004 Kluwer Academic Publishers.