热输入对5A06-6061铝合金搅拌摩擦焊接头断裂特征的影响

Effect of heat input on fracture behavior of friction stir welded 5A06-6061 aluminum alloy joints

在自然冷却和压缩空气强制冷却条件下,搅拌摩擦对接焊接5A06-H112和6061-T651异种铝合金,借助单轴拉伸、纳米压入和显微观测手段,研究热输入对接头拉伸断裂特征的影响规律,揭示其影响机制。结果表明:当转速焊速比(γ)为1.5 r/mm(热输入过低)时,焊核区材料因混合不充分形成S线缺陷,导致接头沿此缺陷在焊核区发生脆性断裂;当转速焊速比达到3.0 r/mm后,焊核区材料混合充分,韧性断裂均发生在6061侧的热影响区。随着热输入增加,断裂角度由41°逐渐减小至3°,断裂类型由切断断裂演化成正断断裂。纳米压入硬度分布显示6061侧的热影响区为接头的弱化区域,该区域的宽度和倾角直接影响断裂角度。断口微观形貌分析表明,抑制热输入有助于增大断裂角度,使接头以切断断裂为主,从而产生更多剪切韧窝,提高接头的断裂伸长率。

To investigate the influence of heat input on the fracture behavior of the joints,the 5A06-H112 and 6061-T651 aluminum alloys were friction stir welded in both nature cooling and forced air cooling.When the ratio of rotational speed to transverse speed is 1.5 r/mm,the materials in the nugget zone were insufficiently mixed to form a kissing bond,resulting in brittle fracture along this defect.As the ratio reaches 3.0 r/mm,the materials in the nugget zone were well mixed,and ductile fracture occurs in the heat affected zone of 6061 aluminum alloy.With the increase of heat input,the fracture angle gradually decreases from 41°to 3°,and the fracture mechanism changes from shear fracture to normal fracture.The distribution of nanoindentation hardness of the FSW joints indicates that the heat affected zone of 6061 aluminum alloy is the weakest area,and the fracture angle of the joint is directly influenced by the width and angle of this weakened area.SEM images of the fracture surface reveal that supressing the heat input could increase the fracture angle and cause shear fracture,which is conducive to form more shear dimples on the fracture surfaces to improve the elongation of the joints.