Selective Etching Procedure for Observation of Primary Silicon Morphologies in V-AlSi20 Master Alloy
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Abstract
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.
Kurzfassung
Aluminiumgussteile mit Siliziumgehalt oberhalb des Eutektikums werden zu einem immer wichtiger werdenden Produkt. Sie entsprechen, insbesondere in der Automobil- und Luftfahrtbranche, einer Vielzahl an technischen Spezifikationen im High-End-Bereich. Ihre hervorragenden Eigenschaften sind in höchstem Maße von ihrem Gussmikrogefüge abhängig. Konventionelle Gießverfahren führen zu großen Primärsiliziumpartikeln in vielfältigen Morphologien. Dies führt beim Zerspanen dieses Werkstoffes zu einer drastisch verkürzten Werkzeuglebensdauer, auf Grund dessen im Bereich der Schmelzeveredelung/Feinung der Schmelze fortwährend geforscht wird. Es wurde gezeigt, dass ein Verfahren utraschallunterstützten chemischen Tiefätzens primäre und eutektische Siliziumkristalle differenziert offenbaren kann, wobei deren räumliche Verteilung bei der Ausscheidung aus dem Eutektikum während der Erstarrung erhalten bleibt. Mittels Rasterelektronenmikroskopie wurden in einer Legierung im Gusszustand verschiedene polyedrische Wachstumsmorphologien, überwiegend gröbere Plättchen, sternförmige und blockartige Strukturen beobachtet. Da diese metallurgische Probenbearbeitung bis zu einem gewissen Grad ortsaufgelöste Informationen zur Morphologie und der Verteilung der Siliziumkristalle liefert, eignet sie sich zur Beurteilung der Leistungsfähigkeit von Veredelungsverfahren/Feinungsverfahren beim Erzielen feiner und gleichmäßig dispergierter Siliziumpartikel in der eutektischen Phase.
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© 2014, Carl Hanser Verlag, München
Articles in the same Issue
- Contents/Inhalt
- Contents
- Editorial
- Editorial
- Technical Contributions/Fachbeiträge
- Selective Etching Procedure for Observation of Primary Silicon Morphologies in V-AlSi20 Master Alloy
- Microstructural and Nanostructural FE-SEM, TEM, and STEM Investigations of High Strength Boron-Alloyed Steel Used in the Automotive Sector
- Failure of Large High-strength Fasteners by Hydrogen Embrittlement
- Conference Report – Microscopy & Microanalysis 2014
- Meeting Diary/Veranstaltungskalender
- Meeting Diary
Articles in the same Issue
- Contents/Inhalt
- Contents
- Editorial
- Editorial
- Technical Contributions/Fachbeiträge
- Selective Etching Procedure for Observation of Primary Silicon Morphologies in V-AlSi20 Master Alloy
- Microstructural and Nanostructural FE-SEM, TEM, and STEM Investigations of High Strength Boron-Alloyed Steel Used in the Automotive Sector
- Failure of Large High-strength Fasteners by Hydrogen Embrittlement
- Conference Report – Microscopy & Microanalysis 2014
- Meeting Diary/Veranstaltungskalender
- Meeting Diary
