Porosity is a defect that often occurs in aluminum alloy casting which is difficult to avoid, and is the most serious problem in aluminum casting. Porosity that occurs during the casting process results in decreased product quality or the product must be recycled. Generally, porosity in aluminum alloys is caused by dissolved and entrapped hydrogen, or underfeeding. Degassiing is the process of binding hydrogen compounds that occur in the aluminum metal smelting process. Inert gases (Argon, Nitrogen, Helium) as inert gases are widely used for the degassing process in aluminum smelting. Its function is as a shielding gas to minimize the porosity that occurs when molten aluminum becomes solid. The process of smelting and manufacturing casting products using used aluminum is carried out using an LPG gas-fired smelting furnace. The degassing process in this study was carried out using Argon gas, which was put directly into the aluminum melt some time after the aluminum melted at 660°C. As long as Argon gas reacts with Hydrogen gas bubbles will form that appear to the surface. The test samples consisted of 6 cylinders with a diameter of 30 and a thickness of 20 mm, made from used aluminum castings, which in the process of making casting products used 500 grams of used aluminum with varying discharges of Argon gas, 0 ; 0.25 ; 0.5 ; 0.75 ; 1 ; 1.25 liter/minute. The test sample was initially observed visually, then several tests were carried out, including: hardness test, density and porosity test, morphology/microstructure test using an optical microscope, SEM-EDAX. Based on the results of observations and laboratory tests, it is known that the porosity of aluminum casting products decreases with increasing use of Argon gas in the degassing process, and also increases the density and hardness of casting products. The addition of Argon gas to melted aluminum increased the hardness of aluminum by 8,52 %.