Evaluation of the formation of intermetallic compounds at the intermixing lines and in the nugget of dissimilar steel/aluminum friction stir welds

Abstract

A relatively successful dissimilar joint between 1050 pure aluminum and annealed low carbon steel is achieved by using friction stir welding. Most studies of joining aluminum to steel have been performed by using low rotational speed with high traverse speed to minimize heat in weld zones and to minimize the thickness of the intermetallic compounds (IMCs). Although the minimized heat may reduce the formation of brittle IMCs but the steel side may not be strongly influenced by this heat which affects the stirring action on both sides. The novelty of this analysis is applying great generated heat by employing a combination of a low traverse speed and a high rotational speed to accomplish the joints. In this study, a high rotational speed of 1550 rpm, a low traverse speed of 17 mm/min, a tilt angle of 1°, a pin length of 1.6 mm, and a deep shoulder surface penetration of 0.2 mm on 1.9 mm sheet thickness is the best set obtained to maximize both the frictional heat and the joint strength. The theory used exhibits more stirring of steel on aluminum than previous studies. The major contribution obtained from this study is knowing a new evaluation of the effect of the thicknesses of the IMCs formed at the interface and on the nugget. It is shown that the effect of the thickness of IMCs formed has a very little impact on the joint strength of about 1.3% at a very high difference in the IMCs thickness obtained between 7.5−8 μm and 8−36 μm. The joint strength depends on how the wide intermixing of steel edge on the aluminum side creates and the size/shape of steel particles.

Keywords

• Friction stir welding
• Intermetallic compounds
• Brittle feature
• Tilt angle
• Strength