Characteristics of the Dissimilar AA7075 and Q235 Steel Joints Fabricated by Friction Stir Welding
Characteristics of the Dissimilar AA7075 and Q235 Steel Joints Fabricated by Friction Stir Welding
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DOI：
10.3390/met12081376
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发表时间：
2022-08
期刊：
影响因子：
2.9
通讯作者：
Yu Chen;F. Zhang
中科院分区：
文献类型：
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作者：
Yu Chen;F. Zhang
本研究采用搅拌摩擦焊（FSW）成功制备了异种AA7075/Q235钢接头，将熔核区（NZ）的AA7075晶粒细化并与破碎的Q235碎片（即钢颗粒、钢条、钢块）混合。同时，由于Al/钢扩散的发生，沿铝/钢（Al/钢）界面产生了金属间化合物（IMC）层。结果还表明，焊接热输入不同，焊接接头的宏观组织和微观组织也不同；在冷搅拌摩擦焊条件下，由于NZ内物质流动微弱而混沌，导致焊接热输入减少，晶粒细化不均匀；Al的动态再结晶只发生在缺乏大钢块的区域。相反，增加焊接热输入可以促进晶粒细化的均匀化，增加IMC层的厚度。FSW质量同时受IMC层厚度和钢片尺寸的双重控制。强化接头既需要最佳厚度的IMC层（约2 μm），又需要细钢颗粒，通过制造上述组织可使接头的抗拉强度提高30 MPa以上。不幸的是，所有FSW接头都以脆性方式失效，伸长率低于5%。在NZ内部观察到两种类型的断裂面：一种是沿Al/钢界面的平坦断裂面，另一种是由于大型钢带和钢块的拔出而导致的不均匀断裂面。
In this study, dissimilar AA7075/Q235 steel joints were successfully fabricated by friction stir welding (FSW), and the grains of AA7075 in the nugget zone (NZ) were refined and mixed with the broken Q235 fragments (i.e., the steel particles, strips, and blocks). Meanwhile, intermetallic compound (IMC) layers were generated along the aluminum/steel (Al/steel) interface due to the occurrence of Al/steel diffusion. The results also revealed that the macro- and microstructures of the FSW joints varied depending on the welding heat input; under the cold FSW condition, micro-defects formed because of the weak and chaotic material flow in the NZ, reducing the welding heat input gave rise to inhomogeneous grain refinement; and the dynamic recrystallization of Al only occurred in the regions that lacked large steel blocks. In contrast, elevating the welding heat input led to the homogenization of the grain refinement and increased the thickness of the IMC layers. The FSW quality was controlled by both the thickness of the IMC layers and the size of the steel fragments simultaneously. Both the optimal-thickness IMC layers (about 2 μm) and fine steel particles were required to strengthen the joints, and a more than 30 MPa increment in the tensile strength could be obtained by manufacturing the above microstructures. Unfortunately, all the FSW joints failed in a brittle manner and the elongation was lower than 5%. Two kinds of fracture surfaces were observed inside the NZ: one was flat along the Al/steel interface, and the other was uneven due to the pulling out of the large steel strips and blocks.