Abstract
This study investigated the effect of the friction stir welding rotation rate and welding speed on the quality and properties of the dissimilar joints between aluminum and carbon steel. Plates of 4 mm thickness from both AA2024 and AISI 1018 were successfully friction stir butt welded at rotation speeds of 200, 250, and 300 rpm and welding speeds of 25, 50, and 75 mm/min. The joint quality was investigated along the top surface and the transverse cross-sections. Further investigation using scanning electron microscopy was conducted to assess the intermetallic layers and the grain refining in the stir zone. The mechanical properties were investigated using tensile testing for two samples for each weld that wire cut perpendicular to the welding direction and the hardness profiles were obtained along the transverse cross-section. Both the top surface and the transverse cross-section macrographs indicated defect free joints at a rotation rate of 250 rpm with the different welding speeds. The intermetallic compounds (IMCs) formation was significantly affected by the heat input, where there is no formation of IMCs at the Al/steel interfaces when higher traverse speed (75 mm/min) or lower rotation speed (200 rpm) were used, which gave the maximum tensile strength of about 230 MPa at the low rotation speed (200 rpm) along with 3.2% elongation. This is attributed to the low amount of heat input (22.32 J/mm) experienced. At the low traverse speed (25 mm/min and 250 rpm), a continuous layer of Al-rich IMCs FeAl3 is formed at the joint interface due to the high heat input experienced (79.5 J/mm). The formation of the IMCs facilitates fracture and reduced the tensile strength of the joint to about 98 MPa. The fracture mechanism was found to be of mixed mode and characterized by a cleavage pattern and dimples. The hardness profiles indicated a reduction in the hardness at the aluminum side and an increase at the steel side.
Highlights
IntroductionAluminum alloys and steels are required to be welded together in a number of industrial applications when weight reduction is needed
Figure shows joints welded rpm rotation speed and different traverse welding speeds are successfully joined without defects such as porosity and cracks (Figure 3a–c)
The top surface is smooth, with some flashes observed in both steel and Al sides
Summary
Aluminum alloys and steels are required to be welded together in a number of industrial applications when weight reduction is needed. It is a challenge to produce dissimilar metal joints using conventional fusion welding techniques because of enormous variations in their melting temperature, mechanical, and physical characteristics, as well as the large amounts of brittle intermetallic compounds (IMCs) formed [1,2,3,4]. Inhomogeneous solidification microstructure, segregations and complex weld pool shapes are appeared after the process and the severely low solubility of Fe in Al which creates excessive. Al-rich Fex Aly IMCs [5,6]. These IMCs deteriorate the mechanical properties [5] and lead to the rapid fracture of the joints [7].
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