Effect of Degassing Time and Cooling Rate on Microstructure and Porosity of Aluminum 6061 Alloy Using Sand Casting Method

Abstract

This research is aimed to get a better understanding on the effort of reducing the porosity level in aluminum alloys. The degassing process (2, 5 and 8 minutes) is done to reduce the hydrogen content in liquid aluminum and cooling rate modifications (13 °C / min, 20 °C / min and 26 °C / min) was performed to reduce the porosity by reducing the size of Dendrite Arm Spacing (DAS). The casting method used in this research is sand casting and raw materials were melted using an electric furnace at 720 °C. The microstructural images showed the DAS size are decreased by size from 137.3 μm to 87.58 μm obtained from cooling rates of 13 °C / min and 26 °C / min respectively. In the other hand, the level of porosity is also decreased from 3.58% at 2 min degassing and the cooling rate of 13 °C / min to 1.8% at 5 min degassing and 26 °C / min cooling rate. Furthermore, the tensile test results show that the value of tensile strength increases when the DAS size and porosity level are smaller. The highest ultimate tensile strength value is 105.9 and the lowest is 70,53 MPa.