Abstract
A dissimilar AA7075/Q235 butt-lap joint was fabricated via ultrasonic-assisted friction stir welding (UaFSW), and the characteristics of the UaFSW joint were investigated systematically. The acoustoplastic effect of the ultrasonic vibration led to the softening of the materials and enhanced the material flow during welding, decreasing the volume of welding defects in the nugget zone of the UaFSW joint. With the help of ultrasonic vibration, a smooth and thin intermetallic compounds (IMCs) layer could generate along the Al/steel interface at the top of nugget zone, which possibly consisted of Al5Fe2 and Al13Fe4 phases. However, the positive effects of the ultrasonic vibration were weakened at low temperatures; consequently, the IMCs layer became discontinuous at the bottom of the nugget zone and the welding defects also formed. The ultrasonic vibration accelerated the dynamic recrystallization and refined the microstructures in the nugget zone due to the increased strain rate and stored energy. As a result, the UaFSW joint exhibited a better mechanical performance in comparison to the FSW joint, and the increment in the peak tensile load/elongation was more than twice. In addition, the UaFSW joint failed in the nugget zone along with the Al/steel interface, and the fracture mode was a mixture of ductile and brittle.
Highlights
Al/steel hybrid components have been widely applied in the transportation system, aimed at reducing both the weight and the fuel consumption of vehicles [1,2].fabricating the dissimilar Al/steel joint is still full of challenges due to the differences between physical and chemical properties [3,4]
Fabricating the dissimilar Al/steel joint is still full of challenges due to the differences between physical and chemical properties [3,4]
The limited solid solubility of aluminum and steel leads to the formation of brittle intermetallic compounds (IMCs), and the excessive growth of IMCs deteriorates the mechanical performance of
Summary
Al/steel hybrid components have been widely applied in the transportation system, aimed at reducing both the weight and the fuel consumption of vehicles [1,2]. Elnabi et al [9] successfully joined AA1050 and low-carbon steel by FSW, observing the formation of IMC layers using different welding parameters. Liu et al [10] joined dissimilar AA6061 and ASTM A36 steel without welding defects, analyzing the effects of FSW conditions on the Al-Fe interfacial transition layer development. Wang et al [11] friction stir welded AA5083 and HSLA-65 steel and built the relationship between the thickness of IMC layers and the tensile properties of the FSW joint. A modified FSW technology called ultrasonic-assisted friction stir welding (UaFSW) is proposed by Ji et al [16] and Wu et al [17], which can be an effective way to elevate the welding quality of a dissimilar Al/steel joint further. UaFSW and (II) revealing the effects of UaFSW on the dissimilar Al/steel butt-lap joint
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