Abstract: There is disclosed an improved process for treating molten aluminum or aluminum alloys containing impurities, such as alkali metals, alkaline earth metals and hydrogen, to reduce the amount of impurities contained therein by in-line rotor degassing. The process comprising the sequential steps of: (a) contacting said molten aluminum or aluminum alloy with chlorine gas by rotor injection; and (b) contacting the molten aluminum or aluminum alloy with a mixture of chlorine gas and sulfur hexafluoride gas by rotor injection, wherein the chlorine gas flow rate in step (a) is between approximately 0.005 to 0.025 scfm and the gas flow rate in step (b) is a combination of a sulfur hexafluoride gas flow rate of between approximately 0.012 and 0.032 scfm and a chlorine gas flow rate of between approximately 0.005 to 0.025 scfm and wherein the ratio of sulfur hexafluoride flow to chlorine gas flow in step (b) is between approximately 1.25 and 2.