采用轻质高强Al/Mg异种材料焊接接头是实现构件轻量化的有效途径。针对Al/Mg搅拌摩擦焊过程中材料成分液化容易伴随金属间化合物出现的现象，本项目采用"化被动为主动"的做法，提出在焊缝材料搅拌摩擦出现成分液化，即半固态条件下，利用超声波在液相中形成的声空化效应破碎、弥散生成的金属间化合物,以消除其不利影响。在发明超声辅助半固态搅拌摩擦焊具的基础上，通过系统研究搅拌摩擦产热以及焊缝成分液化的规律、焊缝液化层中的声空化效应及其对金属间化合物的作用机制、半固态焊缝材料的流变行为及其微观组织演变等问题，揭示声场辅助下Al/Mg半固态搅拌摩擦焊接头的形成及微观组织演变机理，为异种材料（如Al/Cu、Al/Fe、Al/Ti等）的可靠连接提供一种新的研究思路。

The application of dissimilar Al/Mg welded joint, which is of light weight and high strength, meets the need of weight saving. To address the problem that constitutional liquation tends to accompany the presence of IMCs during dissimilar friction stir welding of Al and Mg alloys, the current project plans to use the acoustic cavitation effects produced during the propagation of ultrasonic in the liquid weld metal to fragment and disperse the IMCs and thus eliminate their adverse effects. This is a "Passive to Active" approach. Based on the construction of ultrasonic assisted semi-solid friction stir welding system, the relationship between friction stir heat and constituional liquation, the acoustic cavitation effects in the liquid weld metal and their impact on IMCs, Semi-solid rheological behavior of the weld material and evolution of the joint microstructure will be systematically studied in the project, with the aims to reveal the ultrasonic assisted formation of friction stir welded Al/Mg joints and their microstructure evolution mechanism, and provide a new idea on the dissimilar friction stir welding process (e.g. Al/Cu, Al/Fe, Al/Ti alloys).