对由2A14铝合金退火态叉形环和淬火+人工时效态短壳组成的锁底结构（槽深6 mm）进行搅拌摩擦焊，研究了搅拌针长度（4.0~7.0 mm）对接头组织和性能的影响。结果表明：搅拌针长度小于6.0 mm时，接头根部出现未焊透缺陷，搅拌针长度不小于6.0 mm时，短壳一侧焊缝边缘出现“Hook”缺陷，且其高度随着搅拌针长度增加而增大；随搅拌针长度增加，焊核区晶粒尺寸先减小后增大，拉伸性能先增大后减小，搅拌针长度为6.0 mm时，焊核区晶粒尺寸最小，硬度最高，拉伸性能最好；搅拌针长度为4.0 mm时，接头拉伸断口出现分层，呈准解理和韧窝的混合断裂模式，搅拌针长度不小于6.0 mm时，接头呈韧性断裂。

Friction stir welding was performed on a lock bottom structure (groove depth of 6 mm) composed of an annealed fork ring and a quenched and artificial aged short shell of 2A14 aluminum alloy. The influence of pin length (4.0-7.0 mm) on microstructure and properties of the joint was studied. The results show that incomplete penetration defects existed at the root of the joint when the pin length was less than 6.0 mm, and the “Hook” defect appeared on the edge of the weld on the side of the short shell when the pin lenght was no less than 6.0 mm. With increasing pin length, the height of the “Hook” increased. With increasing pin length, the grain size of the weld nugget zone decreased first and then increased, and the tensile properties increased first and then decreased. When the pin length was 6.0 mm, the grain size of the weld nugget zone was the smallest, the hardness was the highest and the tensile properties was the best. When the pin length was 4.0 mm, the tensile fracture of the joint showed delamination, and the joint had a mixed fracture mode of quasi-cleavage and dimple fracture. When the pin length was no less than 6.0 mm, the joint showed ductile fracture.