Keyhole　tungsten　inert　gas　(K-TIG)　welding　is　a　variant　of　TIG　welding,　which　can　largely　improve　the　weld　penetration　depth　by　forming　keyholes　inside　the　molten　pool　during　welding.　However,　K-TIG　welding　is　generally　considered　unsuitable　for　aluminum　alloys　due　to　their　high　thermal　conductivity.　A　novel　double-pulsed　variable　polarity　TIG　(DP-VPTIG)　welding　process　was　employed　and　the　stable　full　penetration　keyhole　welding　of　7　mm-thick　AA2219　aluminum　alloy　was　achieved.　Keyhole　dynamic　evolution　for　DP-VPTIG　was　investigated　based　on　visual　sensing　technology.　Results　indicate　that　in　low-pulsed　peak　stage　of　DP-VPTIG　process,　the　keyhole　forms　under　the　dominant　role　of　the　downward　arc　pressure　against　the　upward　surface　tension　and　hydrostatic　pressure　acting　on　the　surface　of　the　molten　pool,　while　the　keyhole　is　closed　as　the　upward　surface　tension　and　hydrostatic　pressure　become　the　dominant　role　in　low-pulsed　base　stage.　The　periodic　variation　of　low-frequency　pulse　in　DP-VPTIG　process　stimulates　a　periodic　keyhole　behavior　of　＇opening＇　and　＇closing＇　in　the　molten　pool.　The　formation　of　keyhole　is　beneficial　to　the　increase　of　weld　penetration　depth　as　the　arc　moves　downwards　along　the　keyhole　and　directly　heats　the　solid　metal　under　the　molten　pool.　The　keyhole　size　decreases　with　the　increase　of　low-pulsed　frequency.　Copyright　©　2022,　Northwest　Institute　for　Nonferrous　Metal　Research.　Published　by　Science　Press.　All　rights　reserved.