For aluminum alloy casting, degassing is a necessary process for molten metal in order to extract the dissolved hydrogen in the melt. For copper-containing aluminum alloys, a traditional method is that using mixed gas of inert gas and chlorine as degas agent. Because of the toxicity of the gaseous chlorine, the industrial is trying to avoid using it even though this method can contribute to good castings. As a potential solution, the foundry used argon during degassing, however, the castings were unacceptable since the occurrence of defects. The goal of this project is to develop a new green and clean degassing method for copper-containing alloys without the usage of gaseous chlorine. To achieve this goal, identify those defects and figure out the source of those defects are necessary. Totally four hypotheses of the occurrence of defects were supposed and two of them were discussed in this thesis. They are ineffective hydrogen removal and metal-mold reaction. Experiments were set in WPI and Palmer Foundry to investigate defects from samples with different conditions. This thesis collected and discussed the results from experiments, and made the conclusion that whether these two hypotheses contribute to the occurrence of defects.