Modification of detrimental π-Fe phase in Al-7Si-0.6Mg alloy

Abstract

The regulation of the detrimental π-Fe phase has been the primary concern in Al-7Si-Mg cast alloys. In this work, a two-stage solution treatment is conducted for the complete dissolution of the Mg₂Si phase in the low-temperature stage and for manipulating the decomposition of the π-Fe phase in the high-temperature stage. This approach allows for a systematic investigation into the effect of solution temperature on the decomposition behavior of the π-Fe (Al₈Mg₃FeSi₆) phase while avoiding incipient melting. The coarse π-Fe particles form an interconnected and branched structure in the as-cast microstructure, wrapping the α-Al dendritic arms and isolating the α-Al grains. The π-Fe structure underwent subtle change during the solution treatment at 540°C. At the elevated solution temperature of 560°C, the π-Fe phase decomposed into a fine β-Fe phase, accompanied by particle fragmentation and shape change into the granular form. The modification of the π-Fe phase has achieved a simultaneous enhancement in the strength and ductility of the alloy.