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20 mm thick plates of 2519-T87 high strength aluminum alloy have been welded. The effects of the compositions of filier wires, the heat input and the compositions of shielding gas on the mechanical properties and microstructure of the welded joint have been investigated. The results indicate that finer microstructure, better mechanical properties and higher value of hardness of HAZ can be obtained by using lower heat input. The use of Ar/He mixed shielding gas has several advantages over pure Ar shielding gas. With the increase of the proportion of He in the mixed shielding gas, the grain size of the weld metal as well as porosity susceptibility decreases. When the volume ratio of He to Ar reaches 7:3, the porosity and the grain size of weld metal reach the minimum, and the porosity can be further reduced by filling some CO2.