An alternative approach in ceramic shell investment casting of AZ91D magnesium alloy: In situ melting technique

• AZ91D granule was used as melting material for producing investment cast sample.
• Flux mixed with the granule was found necessary to approach the acceptable casting.
• Decreasing heating temperature and using flux suppressed mould–metal reaction.
• Thinner shell mould contributed to successful in situ melting investment casting.
• Shell permeability was not effective in in situ melting AZ91D investment casting.

In this research, the possibility of ceramic shell investment casting of a magnesium alloy using in situ melting technique was explored. AZ91D granules were charged into shell investment mould and in situ melted under various processing parameters including heating temperature, flux application, shell mould thickness and permeability. Scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction techniques were used to characterise the cast samples. Thermal analysis was employed to further investigate the effect of mould thickness on the solidification behaviour of the metal. It was found that mixing flux with the granules not only reduced the temperature at which melting can be achieved, but it also contributed to produce castings with acceptable surface quality. The use of thinner mould provided higher solidification rate, which is believed to favour in situ melting of the granules. It enabled melting of the granules at 650 °C, which in turn helped to suppress the mould–metal reaction and produce castings with good surface quality. Shell mould permeability showed no influence on suppressing the mould–metal reaction at 650 °C.