Microstructure of Strontium-Containing JIS ADC12 Alloy Solidified under Electromagnetic Stirring

In near-eutectic aluminum casting alloys, the influence of melt flow on eutectic evolution and the formation of intermetallic compounds remains less well understood than its effect on α-Al grain refinement. In this study, JIS ADC12 alloy containing strontium was solidified under electromagnetic stirring, and microstructural features were quantified by image analysis to clarify those effects. Electromagnetic stirring increased both the spacing and the area of eutectic silicon, indicating suppression of the strontium-induced modification. Intermetallic compounds identified as α-Al(FeMn)Si showed pronounced coarsening, accompanied by a morphological transition from Chinese-script to coarse polygonal forms with increasing current frequency. EDS analysis revealed chromium enrichment in the polygonal grains. Thermodynamic calculations revealed that chromium increases the formation temperature of the α-Al(FeMnCr)Si phase, thereby promoting primary grain formation and subsequent coarsening under melt flow. These findings indicate that externally driven melt flow adversely affects the eutectic refinement induced by chemical modifiers and promotes the grain coarsening of primary intermetallic phases in ADC12 alloy.