Vertical　material　flow　and　microstructure　evolution　were　investigated　by　the　material　tracing　technology　during　friction　stir　lap　welding　of　6061-T6　aluminium　alloys　from　a　new　perspective:　various　angles　of　keyhole　obtained　by　emergency　stop　technique.　First,　lamellar　grains　were　transformed　into　equiaxed　subgrains,　and　texture　was　transitioned　from　110//shear　direction　fibre　texture　to　strong　B/(B)　over　bar　components　when　materials　flowed　from　the　advancing　side　to　the　leading　side.　Then　subgrains　grew　into　recrystallised　grains　at　the　retreating　side.　After　that　the　downward　material　flow　at　the　trailing　side　induced　plastic　deformation,　resulting　in　many　subgrains　with　strong　A/(A)　over　bar　texture　components.　Finally,　grains　grew　up　and　retained　with　strong　A/A　components　in　the　stir　zone.