HIGHLIGHTS ON THE ROLE OF Fe, Sr, AND SOLIDIFICATION TIME ON FORMATION IN Al-Si CAST ALLOYS

The present study was undertaken to elaborate on the parameters controlling the microstructural characterization of A319.2 Al-Si alloys, as a function of iron content (0.12-0.8%), Sr addition (similar to 250 ppm), and solidification time (586s vs 513s). For comparison, selected conditions were applied to A356.2 alloys. The use of a hot graphite mold and an end-chill mold provided different solidification rates along the liquid/solid interface, corresponding to DAS values in the range of similar to 23-85 mu m, corresponding to levels of 5, 10, 30, 50, and 100 mm above the chill end. Addition of strontium leads to fragmentation of beta-Al5FeSi platelets. Under similar Fe level and solidification rate conditions, the A319.2 alloys exhibit larger pore sizes than the A356.2 alloys, due to the absence of the (Al-Al2Cu) reaction in the latter and hence longer solidification time. Four types of iron intermetallics were reported viz., delta-, alpha-, beta-, and pi-phases.