Control of Amount of α-Al Phase Particles in near Eutectic Al-Si Alloy by Electromagnetic Stirring

Al-Si alloy is widely used as a casting alloy. The α-Al phase in the semi-solid state has low Si content in the Al-Si alloy. Then by separation of these α-Al phases from semi-solid Al-Si alloy, refining of aluminum can be possible. But, in near eutectic Al-Si alloy, few primary α-Al phases can be crystallized. If the fraction ratio of the α-Al phase can be increased, near eutectic Al-Si alloy can refine, and this method can be used for recycling. In this study, the effect of electromagnetic stirring (EMS) on the microstructure, especially the amount of the α-Al phase particles was investigated. A rotational magnetic field was applied to JIS ADC12 alloy which has near eutectic content during slow cooling from the liquid state to the solid-state, by using a three-phase AC coil. By applying EMS at solidification, the shape of the α-Al phase became particle shape from dendrite shape, and the amount of α-Al phase particles was increased. Moreover, by applying unidirectional intermittent EMS, the volume fraction of α-Al phase particles was decreased with increasing intermittent applying time. In ADC12 alloy, the primary α-Al phases can be crystallized only 10% generally, but it could be obtained over 40% by applying EMS. This means that the semi-solid slurry of near eutectic alloy with over 40% of fraction solid can be obtained by applying EMS.

Effect of Rotating Magnetic Field on Microstructure in AlCuSi Alloys

The solidification of AlCuSi alloys with Mn and Fe was studied by rotating a magnetic field to understand the effect of melt flow. The specimens solidified with a forced convection, low cooling rate and low temperature gradient. Electromagnetic stirring generated by an electric coil around the specimens caused a transformation from equiaxed dendritic to rosette morphology, occasionally with spheroids and minor dendrites. The transformation was quantitatively observed with a specific surface Sv, that decreased for almost all alloys and marked the flow effect on α-Al. The computer coupling of phase diagrams and thermochemistry (CALPHAD) technique was applied for the calculation of phase diagrams and property diagrams. Forced convection decreased secondary dendrite arm spacing λ2 in almost all alloys, while it increased slightly in one studied alloy. The length of detrimental β-Al5FeSi phases decreased in the alloy, where β starts to precipitate in the presence of α-Al, while increasing in alloys where β starts as first and grows in the fully liquid melt. The average overall dimension of the Mn-rich phases increased in almost all alloys, and the number density decreased under flow. The modification of spacing for AlSi-eutectics and Al2Cu was analyzed. It was found that the occurrence of Al2Cu does not influence the fluid flow and vice versa.

Research on the High Reliable Electromagnetic Stirring Power Supply

A reconstructed topology with fault diagnosis and fault-tolerant control strategy of the two-phase quadrature power supply of an electromagnetic stirring system are proposed to improve the reliability of the system. First, if the back stage inverter is faulty, the topology will be reconstructed after the diagnosed fault. The reconstructed topology with the fault diagnosis can be applied twice. Additionally, a fault pulse reset method is proposed to form a fault-tolerant control strategy, for which the high-reliability electromagnetic stirring power supply does not need to switch the control algorithm before and after the failure. The reliability of the electromagnetic stirring power supply is improved greatly. Finally, simulations and experiments verify the correctness of the electromagnetic stirring power supply fault diagnosis algorithm, reconstruction topology, and its fault-tolerant control strategy proposed in this paper.