Papers by Author: Masayoshi Dohi

Abstract: Both rapid and stable semi-solid slurry preparation of hypereutectic Al-14.8%Si-4.5%Cu-1.1%Mg alloy (in mass%) with fine solid granules as well as finely dispersed primary silicon particles was tried using a simple method newly developed, where the low-superheat melt passes through a gap between a rotating regular octagonal rotor and a circumscribed chill block. By examining effects of melt temperature running out from tundish, gap distance and rotational speed of rotor on solidification structure of the semi-solid slurry manufactured, the optimum making condition of the targeted semi-solid slurry was found out. Mean sizes of solid granules and primary silicon particles within the slurry, which had been made quickly with the good reproducibility, were 45μm and 20μm, respectively. Subsequently the obtained semi-solid slurries were rheocast into a cylindrical shape cavity by the use of a high pressure casting machine. It has been shown that the rheocast samples have peak hardness value between the gravity casting and the hot-extrusion, but a good age-hardenability somewhat higher than that of gravity casting.

Abstract: Rheo-extrusion of hypereutectic Al-14.8%Si-4.5%Cu-1.1%Mg (in mass%) alloy which is considerably difficult to hot-extrude was tried using semi-solid slurry with fine solid granules and almost finely dispersed primary Si particles, made by a newly developed rotor process. Trials of rheo-extrusion at the constant extrusion ratio of 36 using this semi-solid slurry were carried out at the different conditions of the extrusion temperature and the ram speeds ranging from 520 to 560oC and from 5 to 20mm/s, respectively. Under the all rheo-extrusion conditions, this semi-solid slurry could easily be rheo-extruded to the round bars of 6mm diameter with sound surface at much lower extrusion force than that of hot-extrusion at very low extrusion ratio. In addition, the characteristic age-hardening behavior which is thought to be essential for the rheo-extrusion process has been found out, namely the peak hardness values of aged bars rheo-extruded at 520 and 540oC were considerably higher, 30HV at maximum, than that of a gravity casting.