The Microstructural Study of in Situ Al Alloy 319 Based Composite Reinforced by Iron-Based Intermetallic Produced by Stir Casting Process

The effect of stir casting process on the modification of the Fe-containing intermetallics formed in a cast in-situ composite based on Al-319 matrix alloy was studied in the present work. Microstructural observations using optical and scanning electron microscopes showed that the undesirable needle-like shape of the Fe-containing intermetallics (β) and also the coarse star-like α compounds were modified into the disc and spheroid shape particles with much less length to width ratio. The effect of parameters such as stirring temperature, cooling rate and Fe contents on the shape, size and distribution of intermetallic particles and eutectic Si blades were also studied. Results showed that the best condition to improve the shape, size and distribution of intermetallic particles can be achieved at a stirring speed of 1200 rpm for 5 minutes at the vicinity of β needles nucleation temperature followed by casting into a metallic mold. Based on the results obtained from the current work, it can be concluded that the harmful morphology of the β intermetallic needles can be properly modified by applying a shearing force during stirring the molten alloy in the semi-solid state.