Microstructure and properties of rheo-HPDC Al-8Si alloy prepared by air-cooled stirring rod process

A new and effective semisolid slurry preparation process with air-cooled stirring rod (ACSR) is reported, in which the compressed air is constantly injected into the inner cavity of a stirring rod to cool the melt. The slurry of a newly developed high thermal conductivity Al-8Si alloy was prepared, and thin-wall heat dissipation shells were produced by the ACSR process combined with a HPDC machine. The effects of the air flow on the morphology of alpha(1)-Al particles, mechanical properties and thermal conductivity of rheo-HPDC samples were studied. The results show that the excellent slurry of the alloy could be obtained with the air flow exceeding 3 L/s. Rheo-HPDC samples that were produced with the air flow of 5 L/s had the maximum UTS, YS, elongation, hardness and thermal conductivity of 261 MPa, 124 MPa, 4.9%, HV 99 and 153 W/(m.K), respectively. Rheo-HPDC samples show improved properties compared to those formed by HPDC, and the increasing rates of UTS, YS, elongation, hardness and thermal conductivity were 20%, 15%, 88%, 13% and 10%, respectively.