铝锂合金机器人搅拌摩擦焊接头组织和性能

为降低焊接压力以适应机器人搅拌摩擦焊接的需求，采用小尺寸轴肩，在较低焊接载荷下进行搅拌摩擦焊接试验. 以单位面积焊缝热输入相同为控制原则，研究了搅拌头轴肩尺寸对2 mm厚2060-T8铝锂合金搅拌摩擦焊接过程压力、焊缝成形、接头微观组织及力学性能的影响. 结果表明，随着搅拌头轴肩尺寸的减小，所需焊接压力呈非线性下降，且稳定焊接过程中载荷振幅值降低. 当轴肩尺寸为4 mm时，焊缝表面形成较大飞边，且接头内部产生孔洞缺陷，当轴肩尺寸大于6 mm时，能获得表面成形良好且内部无缺陷的接头. 当轴肩尺寸为6 mm时，焊接压力为2 800 N，焊核区平均晶粒尺寸为0.52 μm，接头抗拉强度达到最大为396 MPa，为母材的74.1%，显微硬度呈“U”形分布，断裂位置为焊核区，断裂方式为韧—脆混合型断裂.

Structure and properties of friction stir welding joint of Al-Li alloy

In order to reduce the welding pressure and meet the demand of robot friction stir welding, the friction stir welding test was carried out with small size shoulder and lower welding load. With the same heat input per unit area as the control principle, the effects of the shoulder size of the stirring head on the pressure, weld shape, joint microstructure and mechanical properties of 2 mm thick 2060-T8 Al-Li alloy during friction stir welding were studied. The results show that with the decrease of the shoulder size of the stirring head, the required welding pressure decreases nonlinearly, and the pressure amplitude decreases in the stable welding process. When the size of the shoulder is 4 mm, a large flying edge is formed on the surface of the weld and there are holes in the joint. When the size of the shoulder is larger than 6 mm, the joint with good surface shape and no internal defects can be obtained. When the shoulder size is 6 mm, the welding pressure is 2 800 N, the average grain size of the welding core zone is 0.52 μm, the maximum tensile strength of the joint is 396 MPa, which is 74.1% of that of the base metal, the microhardness is “U” type distribution, the fracture position is the welding core zone, and the fracture mode is ductile-brittle mixed fracture.