An　innovative　technology　to　improve　the　bonding　of　refill　friction　stir　spot　welding　by　auxiliary　material　addition　was　proposed.　The　annular　groove　was　eliminated　and　the　energy　absorption　was　increased.　Weld　bonding　was　enhanced　because　the　improved　technology　affected　the　hook,　retractable　line　and　stir　zone　(SZ)　shape　significantly:　(1)　the　effective　bearing　thickness　of　the　welds　increased　as　the　hook　penetration　through　the　sheet　thickness　was　reduced　significantly,　(2)　the　retractable　line　was　eliminated　as　the　dynamic　recrystallisation　was　enhanced　along　the　path　of　the　sleeve　moving　and　(3)　fracture　propagation　was　impeded　by　the　bending　interface　between　the　SZ　and　the　base　materials.