Variation of Mechanical Properties of AlSi20Cu2Ni1 Alloy with Co Addition and Ultrasonic Treatment
The combined effects of the Co addition and Ultrasonic Vibration (USV) on microstructure and properties of Al–20Si–2Cu–1Ni–0.6Mg alloy were studied in this paper. The volume fraction of Co-bearing intermetallic compounds was increased with the increasing of Co content when various levels of Co (from 0% to 1.5%) added respectively into the alloys whether they formed in traditional casting or with USV treatment. The Co-bearing compounds presented as Chinese script or granular when Co was equal or less than 0.7% and turned into dendritic or fish-bone shape when Co was more than 0.7%. USV treatment applied around liquidus temperature of the melt could lead to a refinement of Co-containing compounds by promoting nucleus formation, hindering preferential growth on certain direction, and enlarging solute diffusion coefficient. The addition of equal or less than 0.7% Co, as well as application of USV is very effective in promotion of tensile strength of the hypereutectic Al–Si alloys.