激光高熵化填粉焊接铝/钢异种金属高强韧化机理研究

Dissimilar welding of aluminum-steel is an important method to reduce the weight of automobile parts. But Fe-Al intermetallic compounds can be easily formed in weld seam, which significantly reduce the safety and reliability of Al/steel dissimilar joints. The characteristic, that high entropy effect caused by multi-element metallic systems can inhibit the formation of intermetallic compounds, is used in this project. And an innovative method of laser welding of Al/steel dissimilar metals using high entropy filler powder is proposed. By the design of high mixed entropy of materials in the weld seam, the thermodynamic conditions of Fe-Al intermetallic compounds are changed, and so as to fundamentally inhibit the formation of Fe-Al intermetallic compounds in the weld seam. And then Al/steel dissimilar joints with high strength and toughness can be obtained. In the project, the thermodynamic mechanisms of high mixed entropy inhibiting the formation of Fe-Al intermetallic compounds in weld seam will be explored. The evolution and microscopic mechanism of phase composition, structure and distribution in the high entropy weld seam will be revealed. The regulation model of "mixed entropy – microstructure - joint performance" in the high entropy weld seam will be established. Strengthening and toughening mechanism of laser joints of Al/steel dissimilar metals using high entropy filler powder will be clarified. The project can provide a novelty method to obtain Al/steel dissimilar joints with high strength and toughness. And it also can provide new ideas for dissimilar welding other metals, where intermetallic compounds are easily formed during the welding process.

铝/钢异种金属焊接是实现汽车结构轻量化的重要方式，但两者焊接时焊缝极易生成脆性Fe-Al金属间化合物，显著降低了接头的安全可靠性。本申请利用高混合熵可以抑制金属间化合物生成的特性，提出激光高熵化填粉焊接铝/钢异种金属的新思路，通过焊缝成分的高熵化设计改变Fe-Al金属间化合物生成的热力学条件，从根本上抑制焊缝Fe-Al金属间化合物的生成，进而获得高强韧化的铝/钢异种金属焊接接头。项目研究焊缝高混合熵抑制Fe-Al金属间化合物生成的热力学机制，探索高熵化焊缝物相组成、结构与分布的演变规律及微观机制，建立高熵化焊缝“混合熵值-微观结构-接头性能”的关联模型，阐明高熵化铝/钢异种金属焊接接头的强韧化机理。项目研究结果不仅为铝/钢异种金属高强韧焊接提供了新方法，同时也为其它焊接时易形成金属间化合物的异种金属连接提供了新思路。

铝/钢异种金属焊接是实现汽车结构轻量化的重要方式，但两者焊接时焊缝极易生成脆性Fe-Al金属间化合物，显著降低了焊接接头的安全可靠性。本项目利用高混合熵可以抑制金属间化合物生成的特性，提出激光高熵化填粉焊接铝/钢异种金属的新思路，通过焊缝成分的高熵化设计改变Fe-Al金属间化合物生成的热力学条件，从根本上抑制焊缝Fe-Al金属间化合物的生成，进而提高铝/钢异种金属的可焊接性能。研究发现，高熵化设计的NiCrMnSi0.5CuTi0.5填充粉末通过激光填粉焊接，能够实现DP780双相钢与5083铝合金异种金属的搭接连接。焊缝区内Fe元素含量显著降低，Fe-Al金属间化合物明显减少，但在铝/钢搭接界面存在大量FeAl2和Al2Cu金属间化合物。采用高熵合金粉末FeCoCrNiMn，或通过高熵化设计的CoZnCuMn0.8Si0.2混合粉末，都能实现铝/钢异种金属的良好对接连接。焊缝区形成了高熵效应，且显著抑制了焊缝Fe-Al金属间化合物的产生，但接头铝合金侧存在一个宽度约为10~20 μm的熔合区，该熔合区内没有形成高熵效应，并产生了亚微米级的Fe-Al相。焊后热处理将促进高熵化焊缝的元素扩散，使铝侧母材与焊缝之间过渡区宽度明显增加，Fe-Al相颗粒尺寸也显著增加。焊接时母材局部熔化将改变焊缝初始设定的化学成分与相结构，使高熵化铝/钢异种金属焊接接头硬脆性较明显，但可以通过改变多主元填充粉末的元素组成，或改善被焊工件的坡口形式，调控高熵化焊接接头的力学性能。高熵化焊缝具有优异的耐腐蚀性能与耐摩擦磨损性能。高熵化焊缝填充材料不仅能够运用于铝/钢异种金属焊接，也能够推广至其它异质金属焊接。项目研究结果不仅为铝/钢异种金属焊接提供了新方法，同时也为其它焊接时易形成金属间化合物的异种金属连接提供了新思路。