Porosity Defects Induced by Semi-Solid Isothermal Heat Treatment in Cast Hypereutectic Al-18% Si Alloy

Abstract

The Present study was undertaken to investigate the porosity defects induced by semi-solid isothermal heat treatment in cast hypereutectic Al-18% Si alloy for different holding time. All specimens were heated up to 585 °C then hold for 10, 20, 30 and 40 min. in an electrically heated resistance furnace with heating rate of 10 °C.min-1. After the semi-solid heat treatment, the samples were taken out immediately for water quenching. Bulk density, total porosity and pore sizes at center and edge of each treated sample were investigated. It was found that the porosity in final treated samples increases by increasing the holding time. The pore size increases and the density decreases steeply with increasing the semi-solid isothermal holding time. Above 20 min., holding time the pore size at the edge shows higher value compared with that measured at the center of sample. It might be recommended that shorter holding time during semi-solid isothermal heat treatment should be selected in order to obtain minimum porosity percentage and higher density Al-18% Si alloy castings.