Porosity characteristics of wire arc additive manufactured (WAAM) Al-Cu alloy using different pure argon flow rates and CMT process were investigated. It is observed that the porosity of aluminium alloy deposition can be significantly influenced by pure argon flow rate and CMT process. It is beneficial to reduce the porosity with the increase of pure argon flow rate. CMT-PADV is the most applicable process for aluminium alloy WAAM process. The porosity reduction using CMT-PADV process is due to its low heat input and effective oxide cleanliness of aluminium alloy filler wire. With a proper shielding flow rate of 25 L/min, CMT-PADV process can produce aluminium alloy demonstration with no porosity.