Effect of melt holding on morphological evolution and sedimentation behavior of iron-rich intermetallic phases in Al-Si-Fe-Mn-Mg alloy
(1. National Engineering Research Centre of Near-net-shape Forming for Metallic Materials, South China University of Technology, Guangzhou 510641, China;
2. Guangdong Institute of Materials and Processing, Guangzhou 510650, China;
3. School of Mechanical Engineering, Dongguan University of Technology, Dongguan 523808, China;
4. State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China)
2. Guangdong Institute of Materials and Processing, Guangzhou 510650, China;
3. School of Mechanical Engineering, Dongguan University of Technology, Dongguan 523808, China;
4. State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China)
Abstract: The effect of the melt holding temperature on the morphological evolution and sedimentation behavior of iron-rich intermetallics in Al-7.0Si-1.0Fe-1.2Mn-0.25Mg alloy was investigated using an optical microscope, scanning electron microscope and differential thermal analyzer. The results show that as the holding temperature decreases, the morphologies of the primary iron-rich phase in matrix change from star-like to polygonal, and the number of the primary phases gradually decreases and disappears at 615 °C. Finally, the Chinese script phases with small size, high compact and uniform distribution are obtained. In contrast, the primary iron-rich phases in slag transform into a coarser polygonal shape with lower roundness, and some of them have hollow structures. Furthermore, the area fraction of intermetallics and Fe content in the matrix decrease gradually due to the formation and growth of sludge and subsequent natural sedimentation during melt holding. With the decrease of holding temperature, the main factors hindering the settlement of the primary phases are morphology, size, and density in turn.
Key words: Al-Si alloy; melt holding; iron-rich intermetallic phases; morphological evolution; sedimentation behaviour