Assessment of different techniques for quantification of α-Al(FeMn)Si and β-AlFeSi intermetallics in AA 6xxx alloys

During homogenisation of AA 6xxx aluminium alloys, the platelike beta-AlFeSi intermetallic phase will transform to a less Si-rich and more spheroidised alpha-Al(FeMn)Si phase which is more favourable for extrusion. In this study, several quantitative methods, which determine the relative volume fraction of alpha-Al(FeMn)Si and beta-AlFeSi, are compared and an assessment of each method is made. The methods used are optical microscopy, scanning electron microscopy (SEM) in combination with electron dispersive X-ray (EDX) using polished samples, and X-ray diffraction (XRD) on intermetallics, extracted through selective dissolution of the At matrix. The highest accuracy is obtained by using SEM/EDX analysis and applying two criteria. (C) 2003 Elsevier Science Inc. All rights reserved.