The Effect of Rotating Magnetic Field Induced Melt Flow on the Meso and Microstructure of Unidirectionally Solidified Al – 7wt% Si Alloy

Abstract

During the last two decades, many algorithms have been developed to simulate solidification processing for different casting methods, such as the continuous casting of steel and the direct chill cast of aluminium. Experiments performed in well-known conditions and the detailed knowledge of meso- and microstructures are necessary to validate these simulations. The primary aim of this chapter is to examine the effect of melt flow on the meso- and microstructure of the Al-7wt% Si binary alloy. When developing simulations describing solidification, it is complicated to consider melt flow and its effect on the emerging meso and microstructure. Several experiments are in the literature in which melt probably flowed during solidification. Still, the exact parameters of the experiment and the meso and microstructure formed during solidification are unknown. In this chapter, we present a well - defined experiment and its results, which can be used to validate a simulation that also considers melt flow.

Unidirectional solidification experiments were performed using a rotating magnetic field (RMF) to study the effect of melt flow on the solidified meso- and microstructure of the Al-7wt% Si binary alloy. The samples' first and third 1/3 parts were solidified without magnetic stirring, and the second (middle) 1/3 part was solidified using magnetic stirring. The magnetic induction was 10 mT, the temperature gradient was ~7 K/mm, and the sample movement velocity was 0.1 mm/s. On the longitudinal section of the Sample, the columnar/equiaxed transition (CET), the equiaxed/columnar transition (ECT), the secondary dendrite arm spacing (SDAS), and the macrosegregation (concentration distribution and the amount of eutectic) were investigated. The primary dendrite arm spacing (PDAS) and the grain structure were studied on the cross-section after colour etching. Finally, it is concluded that progressive columnar/equiaxed transition (CET) caused by the magnetic stirring developed between the non-stirred and the stirred part of the sample.