Abstract
The microhardness, precipitated phases and dislocations in the heat-affected zone of friction stir welded joints of 2024 aluminum alloys were observed and analyzed by transmission electron microscopy. The test result indicated that there were some block precipitation particles, Al₇Cu₃Mg₆ phase, in the HAZ close to advancing side. The precipitated phases, AlCu₃ phase, can be observed in the HAZ close to retreating side. Al₇Cu₃Mg₆ phase could enhance the hardness in the advancing side of joint. After FSW, AlCu₃ precipitated phase and high-density dislocations were divided into some fine particles and the lower dislocation density regions, respectively. As a result, the hardness in this region showed the lowest value.

Key words
aluminum alloys, friction stir welding, heat-affected zone, microstructure

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