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Evaluation of alumina as protective coating for carbon fibers in magnesium-based composites

: Abidin, Alfaferi Zainal; Wolf, Michel; Krug, Mario; Endler, Ingolf; Knaut, Martin; Höhn, Mandy; Michaelis, Alexander

Volltext urn:nbn:de:0011-n-3665199 (3.8 MByte PDF)
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Erstellt am: 13.11.2015

20th International Conference on Composite Materials, ICCM 2015. Proceedings. Online resource : 19-24 July 2015, Copenhagen, Denmark
Copenhagen, 2015
Paper 4412-2, 12 S.
International Conference on Composite Materials (ICCM) <20, 2015, Copenhagen>
Deutsche Forschungsgemeinschaft DFG
3D textile reinforced aluminium matrix composites for complex loading situations in lightweight automobile and machine parts (PAK 258); DFG EN 302/2-1
Coating of carbon fibre textile preforms to improve the infiltration properties and stability in aluminum alloys
Konferenzbeitrag, Elektronische Publikation
Fraunhofer IKTS ()
MMC; Al2O3 coating; textile preform; magnesium alloy; GPI

There has been a growing interest in carbon fiber-reinforced magnesium alloy composites (CF/MgAl-MMC) for lightweight applications. Especially in automotive and aerospace industries they offer outstanding mechanical properties combined with low density. Nevertheless, major obstacles in manufacturing of CF/MgAl-MMC are high reactivity and poor wettability of the carbon fibers with molten Mg-Al alloy. Often an undesired formation of carbides (e.g. Al2MgC2 and Al4C3) at the fiber-matrix interface is observed [1]. Another problem is the sensitivity of carbon fibers to the oxidation especially at temperatures of more than 400°C [2]. In order to overcome the major obstacles an alumina protective coating is applied on carbon fiber-based textile preforms. 2D-textile preforms are used which consist of high tenacity (HT) carbon fibers. Atomic layer deposition (ALD) is employed for coating of preforms. The ALD process is performed at a substrate temperature of 220°C and a total pressure of 0.5 kPa using the precursors trimethylaluminum (TMA) and ozone. SEM analysis revealed a conformal and uniform coating with a thickness of 30±3 nm and a good adhesion on carbon fibers (Fig.1). Structure and composition analysis of coated-alumina on planar graphite substrate has revealed an amorphous structure and stoichiometric alumina formation (Al/O atomic ratio ~0.66). The influence of coating on the carbon fibers was investigated by measurement of the tensile strength with single filaments and by determination of the oxidation behavior using TGA analysis. Coated fibers with alumina show a small reduction of the tensile strength of approx. 20%. The TGA results confirm an improvement of oxidation resistance of carbon fibers by alumina coating. The infiltration of the Al2O3-coated 2D-textile preform was performed with Mg-Al alloy AZ91 (9 wt.% Al) by gas pressure infiltration (GPI). A dense composite with completely suppressed carbide formation is received (Fig. 2). This result confirms that an alumina coating works well as protective layer for carbon fibers in metal matrix composites consisting of Mg-Al alloy with high aluminum content.