焊接速度对5754铝合金FSW接头微观组织和力学性能的影响

Effect of travel speeds on microstructures and mechanical properties of friction-stir welded 5754 aluminum alloy sheets

对3 mm厚的5754铝合金板材进行搅拌摩擦焊接,研究了搅拌头在转速800 r/min条件下,不同焊接速度(100~400 mm/min)对搅拌摩擦焊接头微观组织和力学性能的影响.结果表明,5754铝合金FSW接头横截面形貌呈"盆"形.随着焊接速度增加,5754铝合金FSW接头的焊核区和轴肩区的面积逐渐减小,而搅拌针区面积先增加后减小.当焊接速度为300 mm/min时,搅拌针区面积达到最大值6.66 mm^2,轴肩区和搅拌针区面积比例为0.97,5754铝合金FSW接头的强度系数达到97.5%,这主要是因为轴肩区和搅拌针区面积相近,增大了焊核区和热影响区界面面积,从而提高了FSW接头强度,拉伸断裂在焊核区以外(热影响区或基材区),断口为韧性断口.当焊接速度为400 mm/min时,5754铝合金FSW接头的强度系数为58.8%,拉伸试样均断裂在焊核区,断口为脆性断口.

The 3.0 mm thick cold-rolled sheets of 5754 aluminum alloy were prepared by friction stir welding(FSW)at a rotation rate of 800 r/min.The microstructures and mechanical properties of FSW 5754 joints with different travel speeds(100~400 mm/min)were studied.Results showed that the cross section morphologies of FSW 5754 joints were"basin"type.With the travel speed increased,the area of both nugget zone(NZ)and stir-shoulder zone(SSZ)of FSW 5754 joints reduced.While the area of stir-pin zone(SPZ)increased initially and decreased afterwards,peaking at 6.66 mm^2 with the speed of 300 mm/min.At that speed,the area ratio of SSZ to SPZ zone was 0.97,and the strength coefficient of FSW 5754 aluminum alloy joint was 97.5%.These were mainly resulting from the increased interface area between NZ zone and HAZ zone,caused by the similar area between SSZ and SPZ zone.Tensile specimens were all fractured in heat affected zone(HAZ)or base material(BM)with a ductile model fracture.When the travel speed reached 400 mm/min,the strength coefficient of FSW 5754 aluminum alloy joint was dropped to 58.8%.Tensile specimens were all fractured at NZ zone with a brittle model fracture.