中文摘要：

采用左螺纹圆柱搅拌头对 O 态和T4态2024铝合金进行搅拌摩擦焊接试验，研究了材料性能对搅拌摩擦焊焊缝成形的影响，并用软性约束分析了材料性能对焊核尺寸的影响。试验结果表明：焊缝形貌受焊核周边金属约束的影响，约束程度与材料力学性能和温度有关。O 态2024铝合金对接焊时，软性约束体对塑性金属横向迁移的约束小，焊核面积和焊核宽度较 T4态2024铝合金的焊核面积和焊核宽度大。两种热处理状态2024铝合金对接焊时，强度和硬度较高的 T4态2024铝合金置于返回边时，在焊缝两侧、前进边的软性约束体对塑性金属的约束较返回边的软性约束体对塑性金属的约束强，焊核向返回边偏移；由于在返回边有更多的塑性金属，使其沿焊缝厚度方向向上的运动趋势增强，因此返回边的焊核高度较前进边的焊核高度高。对T4态2024铝合金进行适当的预热，会增强焊缝金属的塑化程度，使其向焊缝两侧的迁移运动趋势增强，焊核宽度及面积增大。

英文摘要：

The 2024-O and 2024-T4 aluminum alloy were welded by friction stir welding with col-umn lefthand-thread pins,and the influences of the material properties on the friction stir weld forma-tion was investigated.Soft constraints were applied to explain the impact of the material properties on the size of nugget.The results show that the weld morphology is constrained by the surroundings of nugget,and the constraints are related to material properties and weld temperature.Under the same heat-treated state material,the area and width of the nugget of 2024-O aluminum alloy are greater than that of 2024-T4 aluminum alloy,due to the smaller constraint of lateral migration of plastic met-al by the soft constraint body.While 2024-O aluminum alloy and 2024-T4 aluminum were welded with butt welding,taking the higher strength of 2024-T4 aluminum alloy as the retreated side,the constraint of the advanced side are stronger than the constraint of retreated side by both sides of the welding＆#39; soft constraint body,and the welding nugget is moved to the retreated side;the direction up of movement trend of the welding nugget which is made along the weld thickness is enhanced owing to the more plastic metal of retreated side,the welding nugget height of retreated side is higher than that of advanced side.Under the appropriate preheating conditions of 2024-T4 aluminum alloy,due to the increasing of plasticized metal in the weld and transverse migration of plastic metal,the width and area of the nugget are increased.