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A thermogravimetric study of the oxidative growth of Al2O3/Al alloy composites

Published online by Cambridge University Press:  31 January 2011

K.C. Vlach ,
O. Salas ,
H. Ni ,
V. Jayaram ,
C.G. Levi  and
R. Mehrabian
K.C. Vlach
Affiliation:
Assistant Research Engineer, University of California, Santa Barbara, California 93106
O. Salas
Affiliation:
Graduate Student Researcher, University of California, Santa Barbara, California 93106
H. Ni
Affiliation:
Assistant Specialist, University of California, Santa Barbara, California 93106
V. Jayaram
Affiliation:
Assistant Professor, Indian Institute of Science, Bangalore, India
C.G. Levi
Affiliation:
Associate Professor of Materials and Mechanical Engineering, University of California, Santa Barbara, California 93106
R. Mehrabian
Affiliation:
President, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213
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Abstract

The oxidation of liquid Al–Mg–Si alloys at 900–1400 °C was studied by thermogravimetric analysis (TGA). The development of a semi-protective surface layer of MgO/MgAl2O4 allows the continuous formation of an Al2O3-matrix composite containing an interpenetrating network of metal microchannels at 1000–1350 °C. An initial incubation period precedes bulk oxidation, wherein Al2O3 grows from a near-surface alloy layer by reaction of oxygen supplied by the dissolution of the surface oxides and Al supplied from a bulk alloy reservoir through the microchannel network. The typical oxidation rate during bulk growth displays an initial acceleration followed by a parabolic deceleration in a regime apparently limited by Al transport to the near-surface layer. Both regimes may be influenced by the Si content in this layer, which rises due to preferential Al and Mg oxidation. The growth rates increase with temperature to a maximum at ∼1300 °C, with a nominal activation energy of 270 kJ/mole for an Al−2.85 wt. % Mg−5.4 wt. % Si alloy in O2 at furnace temperatures of 1000–1300 °C. An oscillatory rate regime observed at 1000–1075 °C resulted in a banded structure of varying Al2O3-to-metal volume fraction.

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Articles
Information
Journal of Materials Research , Volume 6 , Issue 9 , September 1991 , pp. 1982 - 1995
Copyright
Copyright © Materials Research Society 1991

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