The　micro-structure　and　residual　stresses　of　VPPA　welds　at　varying　welding　positions　still　lack　systematic　research.　To　clarify　the　effects　of　gravity　on　Al　weld　performance,　7　welding　positions　(from　vertical-up　welding　to　horizontal　welding)　were　used　to　investigate　the　evolution　of　microstructure,　mechanical　properties　and　residual　stresses.　The　results　showed　that　both　micro-structure　and　residual　stresses　of　the　welded　joints　in　non-vertical　up　welding　were　asymmetric　while　those　in　vertical　up　welding　were　symmetric.　The　grain　size　on　the　upper　side　of　the　welded　joints　increased　from　about　66.9　mu　m　for　vertical　up　welding　to　113.9　mu　m　for　horizontal　welding.　Furthermore,　though　lots　of　tear　ridges　and　dimples　appeared　in　all　the　fracture　surfaces,　which　showed　ductile　fracture,　all　fractures　for　non-vertical　up　welding　appeared　on　the　upper　side　of　the　weld.　The　tensile　strength　from　vertical　up　welding　to　horizontal　welding　decreased　from　352.8　MPa　to　319.8　MPa.　In　this　paper,　the　formation　mechanisms　and　underlying　cause　of　the　asymmetric　residual　stresses　and　mechanical　properties　in　non-vertical　up　welding　have　been　analysed　and　discussed.　(C)　2020　The　Authors.　Published　by　Elsevier　B.V.　This　is　an　open　access　article　under　the　CC　BY-NC-ND　license　(http://creativecommons.orgincenses/by-nc-nd/4.0/).