Research on grain refinement and its mechanism of pure aluminum under a novel permanent magnet stirring

Fine, uniform and equiaxed grain structure is one of the most striking features of high-quality Al targets. In general, the imposition of magnetic stirring on the liquid Al during the solidification process is an effective method to promote grain refinement. In the present study, a self–made rotating system of permanent magnets is reported to stir liquid Al during solidification. The temperature change and grain structure of pure Al subjected to a permanent magnet stirring (PMS) are analyzed. The experimental results reveal that the forced convection driven by PMS can lead to a more homogeneous temperature field in the melt. Meanwhile, PMS can greatly refine the grain structure of pure Al and eliminate cavities, but it may induce more gas holes in the ingots. Moreover, a fresh intermittent permanent magnet stirring (I-PMS) approach has been proposed and successfully applied to realize grain refinement of pure Al. Some casting problems can be perfectly solved using suitable processing parameters. Through some valuable experimental works, systematic researches on grain refinement of pure Al under PMS are performed to better understand its refining mechanisms. Therefore, this article further enhances our understanding of related fields and fills the research blank.