Rheo-extrusion of hypereutectic Al-14.8Si-4.5Cu-1.1Mg alloy

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 560°C 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 540°C were considerably higher, 30HV at maximum, than that of a gravity casting.