7075铝合金搅拌摩擦焊接头变形及失效行为

使用搅拌摩擦焊（FSW）设备对厚度为6mm的7075高强度铝合金平板进行对接试验。设计出双径试样，采用液压伺服试验机对7075铝合金搅拌摩擦焊接头进行拉伸试验，并借助奥林巴斯显微镜和扫描电镜观察接头的变形及失效过程。结果表明，7075铝合金搅拌摩擦焊接头在拉伸过程中出现双颈缩现象，颈缩首先在后退侧出现，随着加载的进行，前进侧也出现颈缩现象。微裂纹在接头中的前进侧和后退侧颈缩区内晶界处由微孔洞聚集产生。随着应变的增加，微孔洞数量明显增加，当应变足够大时，微孔洞连接形成微裂纹。微裂纹沿着与加载方向成45°向焊核区进行扩展，导致接头断裂，断裂位置位于接头中的焊核区，断裂方式为剪切断裂混合着微孔聚集型断裂。

Deformation and failure behavior of friction stir weld joint of 7075 aluminum alloy

The butt welding was carried out on the thickness of 6mm 7075 aluminum alloy plate using FSW. The dual diameter samples were designed and tested by hydraulic servo testing machine. The deformation and failure process of FSW joints were observed by Olympus microscopes and scanning electron microscopic. The results show that double necking appears on the FSW joint during the process of loading. The necking firstly appears in the retreating side and then in the retreating side with the progress of loading. Microcracks initiate in the boundary of grain in the advancing side and retreating side by the coalescence of microvoids. With the increasing of strain, the amount of microvoids increases. When the strain is large enough, the microcracks appear due to coalescence of microvoids. The microcracks propagate towards the weld nugget zone along the 45° angle to the loading direction and result in fracture of FSW joints. The location of fracture lie in the weld nugget zone and the fracture mode of the joints is shear fracture mixed dimple.