Effects of rotation tool-induced heat and material flow behaviour on friction stir lapped Al/steel joint formation and resultant microstructure
Effects of rotation tool-induced heat and material flow behaviour on friction stir lapped Al/steel joint formation and resultant microstructure
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DOI：
10.1016/j.ijmachtools.2022.103858
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发表时间：
2022-02-01
影响因子：
14
通讯作者：
Chen, Chuantong
中科院分区：
文献类型：
--
作者：
Geng, Peihao;Ma, Yunwu;Chen, Chuantong
铝/钢搅拌摩擦搭接焊（FSLW）的可靠连接强烈依赖于界面的宏观/微观结构。然而，基本的热机械过程如何影响它们以及如何控制它们仍然不清楚。本文采用三维欧拉-拉格朗日耦合有限元模型结合示踪粒子技术模拟了5052铝合金和高强度DP 590钢的FSLW过程，阐明了工具热和材料流动的作用。结果表明，在轴肩和销轴附近，材料流动主要来自铝的前进侧和钢的后退侧。提高旋转速度会增强整体材料流动，导致钢侧的迁移增加。在较低的旋转速度下，销周围的钢迁移不足是搭接界面处的微空隙和非结合缺陷的主要原因。从前进侧和后退侧分别流出的铝和钢的异步会聚重新填充了瞬时间隙，从而正常地结合销后面的搭接界面。旋转销通过对钢迁移流的剪切和挤压作用，影响钩状结构和钢屑的形成。材料的相互迁移在搭接的Al/钢界面处产生了夹层结构。极高的温度，大约高于Al 5052固相线温度，在引脚底部下导致形成较厚的金属间化合物（IMC），从而大大降低了界面强度。多尺度的机械强度评估表明，具有厚度小于~1.0 μ m的富Al IMC层的插层界面结构是理想的，因为它表现出比Al基体更高的局部界面强度。
Reliable joining of Al/steel via friction stir lap welding (FSLW) is strongly dependent on interfacial macro-/micro-structures. However, how the underlying thermo-mechanical process affects them and how they can be controlled remain unclear. In this study, a 3D coupled Eulerian-Lagrangian finite element model was integrated with a tracer particle technique to simulate the FSLW of Al alloy 5052 and high-strength DP590 steel, to elucidate the role of tool-induced heat and material flow. The results showed that the material flow recirculated near the shoulder and pin, which mainly originated from the advancing side of the Al and the retreating side of the steel. Increasing the rotational velocity intensified the overall material flow, resulting in increased migration on the steel side. Insufficient steel migration around the pin at lower rotational velocities was mainly responsible for the micro-voids and non-bonding defects at the lap interface. The asynchronous convergence of Al and steel flowing from the advancing and retreating sides, respectively, refilled the instantaneous gap, thereby normally bonding the lapped interface behind the pin. The rotational pin affected the hook structure and steel fragment formation through the shearing and squeezing of the steel migration flow. Material inter-migration produced an intercalated structure at the lapped Al/steel interface. The extremely high temperature, approximately above Al 5052 solidus temperature, under the pin bottom caused the formation of a thicker intermetallic compound (IMC), thereby considerably reducing the interfacial strength. Multi-scale mechanical strength assessments indicated that an intercalated interfacial structure with a thickness of Al-rich IMC layer less than ~1.0 mu m was desirable because it exhibited a higher local interfacial strength than the Al matrix.