A preliminary investigation has been carried out into the application of friction stir welding for joining a magnesium alloy to an aluminium alloy. The work has shown that liquation during the welding process can lead to the formation of a brittle intermetallic at the joint interface. This intermetallic has a microstructure composed of a divorced lamellar eutectic containing Al12Mg17 and magnesium. The formation of this microstructure and its influence on mechanical properties are discussed in terms of solidification theory.

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In order to facilitate the development of CaO-Al 2 O 3 based mould flux for casting high aluminium, non-magnetic steel, the effect of CaO/Al 2 O 3 ratios from 0.6 to 3.2 on viscosity and crystallisation characteristics were investigated with the aid of a rotational viscometer, Fourier transform infrared spectroscopy, a single hot thermocouple technique and X-ray diffraction analysis. The results showed that, at temperatures above 1543 K (12708C), the viscosity first decreased and then became stable with increase in the CaO/Al 2 O 3 ratio. At temperatures below 1543 K (12708C), the viscosity again first decreased but then increased, with the CaO/Al 2 O 3 ratio. This viscosity behaviour can be attributed to changes in the network structure characteristics and the precipitation of solid particles within the liquid flux. Increase in the CaO/Al 2 O 3 ratio also first inhibited and then enhanced crystallisation as demonstrated by the changes in initial crystallisation temperatures and incubation times. The X-ray diffraction results confirmed that, at both low and high CaO/Al 2 O 3 ratios, the dominant precipitates were compounds with high melting points. On the other hand, with CaO/Al 2 O 3 ratios in the midrange, the dominant precipitates were compounds with relatively low melting temperatures. It is concluded that mould flux with a CaO/Al 2 O 3 ratio in the range 1.1-1.6 is the most appropriate for casting high aluminium, non-magnetic steels.

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