In-situ observation of eutectic growth in Al-based alloys by light microscopy

An experimental method for the in-situ observation of solidification in eutectic metallic alloys growing at moderate temperatures, i.e. 500-600 degrees C was developed. It is based on unidirectional solidification of thin samples (200 to 700 mu m thick) contained in rectangular quartz glass tubes allowing for in-situ observation of growth on the sample surface by means of light microscopy using a long-distance microscope. The method is illustrated for two-phase eutectic growth in Al-17.5Cu-1.0Ag, Al-11.8Si and Al-11.8Si-0.025Sr as well as for three phase growth in Al-13.3Cu-5.7Si, all at%. Coupled growth of lamellar Al-Al2Cu eutectic in Al-17.5Cu-1.0Ag was investigated in more detail with regard to spacing selection: experiments were performed in a temperature gradient of 38 +/- 1 K cm(-1) using different, but constant withdrawal velocities ranging from 0.025 to 1.8 mu m s(-1). Measured spacing was compared with literature data and discussed with reference to the Jackson-Hunt theory and the recent amendment proposed by Akamatsu, Faivre, Karma and Plapp. In-situ observations were complemented by post-mortem metallographic analysis using SEM and EBSD in transverse sections. (C) 2013 Elsevier B.V. All rights reserved.