中文摘要：

通过单道与双道焊搭接接头试样疲劳试验,对铝合金6061-T6搅拌摩擦焊搭接焊缝缺陷和疲劳性能进行了比较分析.结果表明：搅拌摩擦焊搭接接头连接界面处总存在钩状缺陷,对搭接接头疲劳性能产生严重影响,其疲劳强度不高于母材抗拉强度的5.6％.单道焊试样疲劳性能优于双道焊试样,单道焊和双道焊试样疲劳强度特征值△σk（应力比R=0.1）分别为17.45MPa和13.91MPa,双道焊工艺不能改善钩状缺陷分布特征.单道焊搭接接头疲劳断口为多重起裂,且裂纹源均位于上板底部钩状缺陷处,疲劳裂纹扩展区表现为穿晶断裂特征,具有典型的疲劳条带且存在二次裂纹;双道焊试样起裂位置和二次裂纹数量均比单道焊多,且起裂位置有沿晶断裂特征,是降低其疲劳性能的主要原因.

英文摘要：

The fatigue performances of AA6061-T6 friction-stir-welded overlap joints and influences of welds defects were investigated and comparatively analyzed based on the fatigue experiments of single pass and double pass welded specimens.The results indicate that the hook defects always form at the bonded interface of friction stir overlap welded joints and have seriously influence on the fatigue properties of the specimen.The fatigue strength of overlap joints is less than 5.6％ ultimate tensile strength of the base materials.The fatigue properties of single pass welded specimens are better than that of double pass welded specimens.The characteristic values of fatigue strength Aσk （R =0.1） for single pass and double pass welded specimens are 17.45MPa and 13.91MPa,respectively.The double pass welding methods do not improve the distributive features of hook defects.The fatigue fracture surfaces of single pass lapwelded joints indicate the multiple crack initiations and the fatigue cracks always initiate from the bottom of the upper plate corresponding to the hooking places.The fatigue propagation zones show the transgranular fracture features are mainly characterized by the typical fatigue striations and some secondary cracks.The quantities of fatigue crack initiation positions and secondary cracks for the double pass welded specimens are greater than those of the single pass welded specimens which result in the lower fatigue properties.