Particularities of the Formation and Modification of Si and Mg 2 si as Second Phases in Casting Al Alloys: Use of Shape Descriptors and Fractal Dimension

This work presents an overview on the study of Si and Mg 2 Si, obtained as second phases in aluminum alloys, including their modifications due to processing conditions, alloying elements and heat treatments. These micrometric phases are generally studied using optical microscopy (OM), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Although they can be differentiated combining OM and SEM, a validation study using XRD is indispensable. This work studies the peculiarities of using these techniques, and the differentiation of Si and Mg 2 Si depending on their XRD peaks, morphologies and gray scales. This review showed that the presence of other second phases complicates the identification of Si and Mg 2 Si. It also revealed that their morphological modifications have been barely studied quantitatively. We are presenting some study cases related to this topic, adding our own quantitative characterizations through the use of shape descriptors and fractal dimension, demonstrating their effectiveness and importance.