Abstract: Weld penetration of A-TIG welding reaches above 3 times that of conventional TIG welding for aluminum alloy when multi-component flux AF305 is used as surface activating flux. A-TIG welding with AC, DCEN and DCEP mode are carried out. It is found that, flux has different effects on weld penetration when arc polarity is different. Effect of compelled arc constriction on weld penetration of alternative current welding is studied. It is believed that, constriction of whole arc root is not the main mechanism of AF305 dramatically improving weld penetration, it has relation with separate distribution of slag on weld surface. Then SEM observation and EDS analysis of slag are carried out respectively. Separate distribution of slag on welding pool during welding and great constriction of arc spots are confirmed by TIG welding with helium shielding gas. Relation between slag contribution and weld penetration is studied by adding aluminum powder into AF305 to change this distribution. It is believed that, during welding, separate distribution of slag on welding pool results in great constriction of arc spots, increases of arc spot force and Lorentz force within the arc and welding pool, in the end, increase of weld penetration.

Key words: AC A-TIG welding, Activating flux, Aluminum alloy, Weld penetration