EPMA mapping of small particles of α-AlFeSi and β-AlFeSi in AA6063 alloy billets

Abstract

It is well known that the spatial distribution and the spatial density of the particles oα-AlFeSi and β-AlFeSi in the billets of Al-Mg-Si alloys, such as AA6063 alloys affect the quality of anodizing performance of their extrusions. For this reason it is very important to control the spatial distribution and the spatial density of both AlFeSi particles at extrusion plants. The X-ray diffraction method (XRD) has been used for discrimination between α-AlFeSi and β-ALFeSi particles. However it is not an appropriate method for determining the spatial distributions of particles in the alloys. As an alternative method an electron probe microanalyzer (EPMA) has been used for determining the spatial distributions of each element in the microstructures. However, unfortunately it is difficult to discriminate between the particles composed of the same elements like α-AlFeSi and β-AlFeSi particles. Thus, we tried to develop a convenient method to discriminate between α-AlFeSi and β-AlFeSi particles in the microstructure of AA6063 alloys and developed the EPMA mapping of α-AlFeSi and β-AlFeSi particles. First, in order to discriminate between the two particles, we tried to use the relative X-ray intensity ratio, the I Fe/I Si ratio instead of the Fe/Si mass ratio. Then, we calculated the value of the I Fe/I Si ratio from α-AlFeSi and β-AlFeSi by using Monte Carlo calculations and obtained the critical value of the I Fe/I Si ratio, to distinguish between α-AlFeSi and β-AlFeSi. After that, using the discrimination value, we developed the EPMA mapping program (EPMA method) to observe the distributions of α-AlFeSi and β-AlFeSi, and to calculate the areas (%) of α-AlFeSi and β-AlFeSi. Finally, we checked the correlation between the EPMA and the XRD methods. Consequently, the two methods were in good agreement. Today, this EPMA method instead of the XRD method is successfully used in the quality control of 6063 aluminum alloy billets after heat treatment at our aluminum extrusion works.