Effect of Semi-Solid Rotating Container Process on Characteristics of Solidification, Dendrite Coherency and Microstructure of AZ91 Magnesium Alloy

The purpose of this study was to investigate the effect of the semi-solid rotating container process (RCP) on the characteristics of solidification of AZ91 magnesium alloy and its relationship with microstructure morphology. Thermal analysis (CA-CTA) performed under controlled conditions along with semi solid casting process. Rotation of the container, caused decrease in solidification temperature up to maximum 14°C. However, this effect has been much more limited on nucleation temperature of primary α-Mg phase. The temperature of solidification range increased to a maximum of 16 °C, which led to a better control of the semi-solid process. Comparison of the results between fraction of solid and microstructure showed that rotation with 150 RPM is unable to create an effective fluid flow, in spite of low cooling rate. Rotating with 210 RPM, caused sharp increase in the cooling rate and reduced the effect of effective fluid flow in the slurry. It has been observed that the balance between the effect of the cooling rate and the effective fluid flow has been created at the rotational speed of 180 RPM. Thus, the least solid fraction and the most desirable quality of the morphology have been achieved in the microstructure. Rotation of the container decreased the temperature to a maximum of 15°C and increased the solid fraction to a maximum of 6 % at dendrite coherency point (DCP). This proved that RCP casting method postponed the DCP and therefore, the defects caused by casting can be reduced.