· Aleaciones ligeras ·
R. Raiszadeh* and W D Griffiths
Department of Metallurgy and Materials Science, The University of Birmingham
67th World Foundry Congress
The change in the volume of an air bubble held within commercially pure
liquid aluminium was recorded by real time x-ray radiography, to estimate
the behaviour of double oxide film defects after entrainment in liquid
aluminium. This showed that first oxygen and then nitrogen were
consumed by the melt to produce Al2O3 and AlN respectively. Varying the
initial hydrogen contents of the melt also showed that hydrogen could
diffuse into the atmosphere within a trapped bubble, and cause it to
expand. A mathematical model was developed using the consumption
rates obtained from this experiment that included the diffusion of
hydrogen, which suggested that the atmosphere within a double oxide film
defect should be consumed by the surrounding Al melt in less than two
minutes.
In addition, a double oxide film-free liquid aluminium melt was poured into
ceramic test bar moulds which then held in the liquid state for 20 minutes.
Study of the fracture surfaces suggested that the two non-wetting surfaces
of a double oxide film defect might bond to each other, after the internal
atmosphere of the film was consumed, and that this could occur in 20
minutes or less.
