Selective etching procedure for observation of primary silicon morphologies in V-AlSi20 master alloy

Aluminium castings with silicon content above the eutectic are becoming an increasingly important product, meeting a wide range of high end engineering specifications, particularly in automotive and aerospace industries. Its outstanding properties highly depend on their cast microstructures; conventional casting will produce large primary silicon particles in a variety of morphologies. This causes drastically shortened tool life when machining this material, reason for which melt refinement is an ongoing field of investigation. An ultrasound assisted chemical deep etching procedure could be proven to reveal primary and eutectic silicon crystals in all detail while preserving the spatial distribution they had when precipitating from the eutectic during solidification. Different polyhedral growth morphologies, mostly coarser platelets, star-like and blocky structures, were observed in an as cast alloy using Scanning Electron Microscopy. As this metallurgic sample treatment provides to a certain extend spatially resolved information about morphology and distribution of silicon crystals, it is suitable to assess the grade of success of refinement processes aiming to achieve fine and well dispersed silicon particles in the eutectic phase.