Thixoformability of hypoeutectic gray cast iron

Hypoeutectic gray cast iron of composition Fe-2.6 wt%C-1.5 wt%Si, specifically developed as a thixoformable raw material, was prepared via conventional casting in sand molds. Samples were heated to the semi-solid state at 1160 and 1180 °C and held at these temperatures for 0, 30, 90 and 120 s to study their morphological evolution. Tests reveal that heating to the semi-solid range changes the morphology of the graphite from A to B type, but does not significantly affect interdendritic arm spacing between graphite lamellae. The resulting structure is composed of fine graphite and pearlite. Two platen compression tests were also carried out in an instrumented eccentric press to examine the material's semi-solid behavior at the same temperatures and holding times. The tests indicated that the semi-solid cast iron behaves like aluminum-silicon alloys, presenting a stress of up to 24 MPa under 80% strain and a corresponding apparent viscosity of up to 1.5 × 105 Pa s at 1180 °C.