Selective matrix dissolution in an Al–Si eutectic

This study investigated the selective matrix dissolution in an Al-Si eutectic alloy, aiming to develop controlledprocedures for modifying its irregular structure and selectively removing the aluminum matrix without affecting silicon. The research context highlights the industrial importance of Al-Si alloys in automotive, aerospace, and engineering sectors, particularly concerning their high fluidity for casting. The methodology involved chemicallymodifying the Al-Si eutectic by adding 300 ppm of strontium, which transformed the initial coarse flake structure into a finer fibrous morphology, thus enhancing its technological suitability. Two electrochemical approaches derived from superimposed Pourbaix diagrams were then explored for selective phase dissolution: anodisation at 0.3 V (SHE) in 1 M HCl and electropolishing in a mixture of perchloric acid and methanol (10:90) at $0^\circC$. Results indicated that anodisationin HCl led to pitting corrosion and was only partially successful after an extended period (20 hours) in dissolving the aluminum, leaving silicon intact. Conversely, electropolishing proved highly effective, achieving both partial and complete matrix dissolution without affecting the siliconstructures. This established a well-controlled method for selective phase dissolution, offering potential applications in studying nucleation, growth mechanisms, and kinetics of transformation in this eutectic alloy, as well as for extracting silicon particles for semiconductor industry use or other applications requiring low density and an excellent electron/mass ratio.