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The main purpose of this study was to investigate the effect of welding parameters on the failure mode and stir zone characteristics of aluminum alloy 2024-T3 joined by friction stir spot welding. The welding parameters in this work are tool rotational speed, plunge depths of shoulder, and pin geometry. In accordance with the methods of previous investigations, the rotational speeds were set to 630 rpm to 2000 rpm. Two pin geometries with concave shoulder were used: triangular and cylindrical. The plunge depths of the shoulder were 0.3, 0.5 and 0.7 mm. The shoulder diameter and pin height for both geometries were 14 and 2.4 mm, respectively. The diameter of the cylindrical and triangular pins was 5 mm. Results show that the parameters mentioned earlier influence fracture mode under tensionshear loading. Two different fracture modes were observed during the examinations. Low-penetration depths and low-rotational speeds lead to shear fracture, whereas high values of these factors cause the tension-shear fracture mode. Fracture of the lower sheet sometimes occurs at high rotational speeds. [ABSTRACT FROM AUTHOR]

In this study, the spot friction welding of 2024-T3 aluminum alloy with 1.6 mm in thickness has been investigated. The effects of the tool rotational speed (630, 1000, and 1600 rpm), shoulder penetration depth (0.3 and 0.7 mm), and pin geometry (cylindrical and triangular shape) have been discussed on the metallurgical and mechanical properties. Results indicated that the pin geometry has a considerable effect on the shape of the stir zone. The results of tensile shear tests showed that the tensile shear load increased with increasing rotational speed in the shoulder penetration depth of 0.3 mm, while high shoulder penetration depth had a bilateral effect on the tensile shear load. In addition, the results showed that the tensile shear load of welds made with the triangular pin at a low rotational speed, and a low shoulder penetration depth was more than of welds made with the cylindrical one, which was attributed to a finer grain size generated in the stir zone. Observation of the failed specimens indicated two types of failure modes under tensile shear loading conditions including the fractures that occurred in the vicinity of keyhole (shear fracture) and the fractures that occurred in shoulder indentation (tensile shear-mixed fracture mode). The microhardness tests with both pins showed that the minimum hardness was measured in the heat-affected zone. [ABSTRACT FROM AUTHOR]

In this work, friction stir spot welding with 1.6 mm thickness of the 2024-T3 aluminum alloy is carried out. The effects of the tool rotational speed and shoulder penetration depth on surface appearance, macrostructure, temperature profile, maximum failure load and failure modes are investigated. Results show that, the effect of the tool rotational speed on maximum tensile shear load is similar to the effect of the shoulder penetration depth, increasing tool rotational speed and shoulder penetration depth resulted in the increase of the tensile shear load. Maximum load of about 8282 N is obtained by using 1000 rpm rotational speed and 0.7 mm shoulder penetration depth. Observation of the failed specimens indicates two types of failure modes under tensile shear loading, the shear fracture that occurs in low shoulder penetration depths and tensile shear fracture that occurs in high shoulder penetration depths. [ABSTRACT FROM AUTHOR]

Highlights: [•] Successful lap joint friction stir welding of AA5456 with two different tempers. [•] New stepped conical threaded pin for FSW of lap joints is introduced. [•] Investigated interactions between tool geometry and mechanical properties. [•] Microstructure and fracture surface analysis of dissimilar lap welds. [Copyright &y& Elsevier]