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金属学报    DOI: 10.11900/0412.1961.2022.00602
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局部强冷作用下厚板铝合金/镁合金搅拌摩擦焊界面金属间化合物的析出行为

徐洋1  柯黎明2  聂浩2  夏春2  刘强2  陈书锦1

1 江苏科技大学 材料科学与工程学院  镇江 212003 2 南昌航空大学 轻合金加工科学与技术国防重点学科实验室  南昌 330063

Precipitation Behavior of Intermetallic Compounds at the Interface of Thick Plate Friction Stir Welded Al Alloy/Mg Alloy Joints Under Local Strong Cooling
XU Yang 1, KE Liming 2, NIE Hao 2, XIA Chun 2, CHEN Shujin 1

1 School of Materials Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China 2 National Defence Key Discipline Laboratory of Light Alloy Processing Science and Technology, Nanchang Hangkong University, Nanchang 330063, China

全文: PDF(3243 KB)  
摘要: 以15 mm厚的5A06-H112铝合金和AZ31B-O镁合金作为研究对象,采用液氮对5A06-H112/AZ31B-O搅拌摩擦焊(FSW)接头上部进行局部强冷,结合EBSD和TEM,研究了空冷和液氮冷却作用下接头界面金属间化合物(IMCs)沿板厚方向上的析出行为。结果表明,2种冷却条件(空冷和液氮冷却)下,接头铝合金侧界面上部和中部附近均析出了大面积的细小Al3Mg2相,而界面底部则为细小的再结晶Al晶粒,晶粒大小由峰值温度和应变速率主导;接头镁合金侧界面存在2种冶金反应机制,其中接头界面上部发生了共晶反应(Mg + Al12Mg17 ↔ Liquid),接头界面中部和底部则是以扩散反应机制主导,析出了由Al3Mg2相和Al12Mg17相组成的双层IMCs。液氮冷却下接头界面附近的峰值温度和高温停留时间均有一定程度的下降,抑制了铝合金侧界面Al3Mg2相长大和镁合金侧界面冶金反应,这与液氮冷却下接头界面的低峰值温度和高应变速率有关。
关键词 搅拌摩擦焊厚板铝/镁接头金属间化合物液氮冷却    
Abstract:Al and Mg, as the lightest structural metals, exhibit high specific strength and excellent damping performance. These attractive qualities render them highly applicable in industries such as automobile, high-speed rail, and aerospace. To further meet the requirements of lightweight structures and different service environments, Al and Mg are combined into a complete structure. When they are joined by conventional fusion welding, pores, cracks, and thick intermetallic compounds (IMCs) form easily due to high welding temperatures. Friction stir welding (FSW), a novel solid-state joining technique, presents a promising alternative. This method possesses several advantages for Al/Mg hybrid structures, primarily due to its welding temperature, which falls below the melting point of the base metal. However, when the thickness of the base metal exceeds 10 mm, Al/Mg FSW weld formation becomes challenging because of the inhomogeneous distribution of IMCs along the thickness direction. The upper segment of the Al/Mg FSW joint develops thick IMCs, while the bottom does not achieve metallurgical bonding. The formation of these IMCs is related to the high temperature due to severe friction and deformation during FSW. Liquid nitrogen is an effective cooling medium that can be applied in FSW. In particular, liquid nitrogen may lower the peak temperature of a thick-plate Al/Mg FSW joint, inhibiting the formation of IMCs during Al/Mg FSW joint formation. This work focuses on 5A06-H112 Al alloy and AZ31B-O Mg alloy, both with a thickness of 15 mm. The upper segment of the Al/Mg FSW joint is cooled by liquid nitrogen. The precipitation behavior of IMCs at the joint interface under air and liquid nitrogen cooling was studied by EBSD and TEM. The results reveal that a large area of fine Al3Mg2 phase precipitates near the upper and middle parts of the Al side interface under two cooling conditions (air and liquid nitrogen), while fine recrystallized Al grains form at the bottom of the interface. The sizes of the Al3Mg2 phase and Al grains are related to the peak temperature and strain rate. The Mg side interface, under both cooling conditions, exhibits two distinct metallurgical reaction mechanisms: the upper segment undergoes a eutectic reaction (Mg + Al12Mg17 ↔ liquid), and the middle and bottom segments primarily experience a diffusion reaction. This results in a eutectic microstructure (Mg solid solution and Al12Mg17 phases) in the upper layer at the Mg side interface. A two-layer IMC structure, consisting of an Al3Mg2 phase and an Al12Mg17 phase, precipitates along the middle and bottom of the Mg side interface. However, compared with the air-cooling condition, the peak temperature and high temperature residence time of the interface under the liquid nitrogen-cooling condition have decreased to a certain extent. This results in a marked inhibition of the growth of the Al3Mg2 phase at the Al side interface and the metallurgical reactions (eutectic and diffusion) at the Mg side interface, which is related to the low peak temperature and high strain rate under liquid nitrogen.
Key wordsfriction stir welding    thick plate Al/Mg joint    intermetallic compounds    local strong cooling
收稿日期: 2022-11-24     
基金资助:国家自然科学基金面上项目
通讯作者: 徐洋   

引用本文:

徐洋 柯黎明 聂浩 夏春 刘强 陈书锦. 局部强冷作用下厚板铝合金/镁合金搅拌摩擦焊界面金属间化合物的析出行为[J]. 金属学报, 10.11900/0412.1961.2022.00602.

链接本文:

https://www.ams.org.cn/CN/Y0/V/I/0

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