Effect of solidification sequence on the microstructure and mechanical properties of die-cast Al-11Si-2Cu-Fe alloy

The effect of solidification sequence on the microstructure and mechanical properties of die-cast Al-11Si-2Cu-Fe alloy is reported. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural evolution at different positions of the same casting. For the thin wall thickness (3 mm), the microstructure of the alloy remains unchanged between the surface and the center of the casting. With the distance from the same surface increasing from 0 mm to 3 mm for the thick wall thickness (6 mm), the volume fraction of primary α-Al phases increases from 76% to 86.6%, the size of primary α-Al phase from 20 μm to 40 μm, the average length of eutectic Si from 3.4 μm to 15.6 μm, the average length of α-AlFeMnSi phase decreases, the brittle β-AlFeSi forms and the volume fraction of porosity rises from 0.017% to 0.328%. These changes contribute to the reduction in the ultimate tensile strength from 300.1 MPa to 210.1 MPa, in the elongation from 1.78% to 0.81%, and the quality index (Q) from 333.7 MPa to 196.4 MPa. A typical brittle fracture is observed on the tensile fracture surface. As the solidification time decreases, the smooth flat areas become small and the amount of tearing ridges increases.