A comparative study of the primary phase formation in Al–7 wt% Si and Al–17 wt% Si alloys solidified by electromagnetic stirring processing. (September 2020)

• Record Type: Journal Article
• Authors: Li, Mingjun; Omura, Naoki; Murakami, Yuichiro; Matsui, Isao; Tada, Shuji
• Is Part Of: Materials today communications. Volume 24(2020)
• Publication Date: 2020-09
• Subjects: Al–Si alloy -- Solidification -- Microstructure -- Refinement -- Electromagnetic stirring; Materials science -- Periodicals; 620.11
• DOI: 10.1016/j.mtcomm.2020.101146
• Languages: English
• ISSNs: 2352-4928

Abstract

Highlights: The primary phase formation in Al–Si alloys was examined by electromagnetic stirring processing. A refinement mechanism was proposed based consideration of differences in electrical resistivity. A low fraction of primary Si solid is sufficient for producing refined grains. Abstract: In the present study, hypoeutectic Al–7 wt% Si and hypereutectic Al–17 wt% Si alloys were solidified using an electromagnetic stirring (EMS) technique. The microstructures were observed as a function of EMS imposition time for both alloys, showing that the primary aluminium solid solution (Al(ss) ) in the Al–7 wt% Si alloy and the primary silicon solid solution (Si(ss) ) in the Al–17 wt% Si alloy could be refined when EMS was imposed for a sufficiently long duration. In addition to the EMS-induced fluid flow, which plays an important role in promoting grain multiplication during solidification, a novel mechanism was proposed to explain the refinement upon considering the significant differences in electrical resistivity between the primary solid and remaining liquid. It was revealed that the primary Al(ss) in the Al–7 wt% Si alloy is mobile and leads the surrounding liquid, whereas the primary Si(ss) in the Al–17 wt% Si alloy is sluggish and lags the counterpart liquid, when EMS is imposed. Although the movement behaviours of these two solids differ greatly, both primary phases can be refined owing to uncoupled displacement, indicating that EMS is effective for refining the primary phases despite the differences in their crystal features. A supplementary quenching experiment of the Al–17 wt% Si alloy below liquidus indicated that even a low fraction of primary Si solid can provide sufficient crystal nuclei to produce refined Si(ss) grains.