-MA 2 As one type of heat-treatable aluminum alloys, AlCu cast alloys arewidely used in transportation, aerospace and military industries owingto their excellent mechanical and physical properties. For the heat-treatable aluminum alloys, the solution heat treatment (SHT) is usually the most important stage to dissolve the second intermetallic phase into (Al) matrix. Tpresent study is focused on the mechanism of solid-state transformation of Fe- rich intermetallics in the squeeze cast Al5.0Cu0.6Mn alloy with variable Fe contents during solution heat treatment. 3 710 5 C 75 Mpa 65 mm 68 mm 250 C 10 mm 20 mm 538 C 4 5 Fe-rich intermetallics of the gravity die cast alloys in as- cast condition: (a) 0.1% Fe; (b) 0.5% Fe; (c) 0.7% Fe; (d) 1.0% Fe; and (e) 1.5% Fe FE-RICH INTERMETALLICS IN SHT CONDITION (12 H): (A) 0.1% FE; (B) 0.5% FE; (C) 0.7% FE; (D) 1.0% FE; AND (E) 1.5% FE 6 XRD PATTERNS OF THE ALLOYS AFTER SHT FOR 12 H: (A) UN-DEEP ETCHED; (B) DEEP ETCHED 7 TEM MICRO-IMAGE AND EDS OF NEW -FE IN THE FE10 ALLOY AFTER SHT FOR 12 H 8 SEMOBSERVATIONS OF THE TYPICAL 3-DMORPHOLOGIES OF THE FE-RICH INTERMETALLICS IN AS-CAST AND SHT FOR 12 H: (A) 0.5% FE, AS-CAST; (B) 0.5% FE, SHT;(C) 1.0% FE, AS-CAST; (D) 1.0% FE, SHT 9 3-D MORPHOLOGY OF -FE BY DEEP ETCHING:(A) 0.5% FE; (B) 1.0% FE 10 MICRO-IMAGE, EDS AND SADP OF (AL) BETWEEN -FE PARTICLES IN THE FE05 ALLOY 11 FE-RICH INTERMETALLICS IN SHT CONDITION FOR FE05 ALLOY: (A) 10 MIN; (B) 2 H; (C) 6 H 12 FE-RICH INTERMETALLICS IN SHT CONDITION FOR FE10 ALLOY: (A) 10 MIN; (B) 2 H; (C) 6 H 13 RELATIVE AREA PERCENT OF -FE WITH DIFFERENT SHT TIMES 14 15 The Chinese script-like -Fe, the Al6(FeMn) and the needle-like Al3(FeMn) phases are metastable after solution heat treatment, which change to the new copper-rich -Fe (Al7Cu2(FeMn)) phases. The TEM and the deep etching images show that the new -Fe phases display a cylindrical structure to minimize their surface area. The transformation of the -Fe and Al6(FeMn) directly produces a two-phase intergrowth of the -Fe and the (Al) phases, the Al3(FeMn) phases will directly change into -Fe, which consumes the Al2Cu phase in the (Al) matrix.