Abstract
In the current study, a 2 mm thick low-carbon steel sheet (A283MâGrade C) was joined with a brass sheet (CuZn40) of 1 mm thickness using friction stir spot welding (FSSW). Different welding parameters including rotational speeds of 1000, 1250, and 1500 rpm, and dwell times of 5, 10, 20, and 30 s were applied to explore the effective range of parameters to have FSSW joints with high load-carrying capacity. The joint quality of the friction stir spot-welded (FSSWed) dissimilar materials was evaluated via visual examination, tensile lap shear test, hardness test, and macro- and microstructural investigation using SEM. Moreover, EDS analysis was applied to examine the mixing at the interfaces of the dissimilar materials. Heat input calculation for the FSSW of steelâbrass was found to be linearly proportional with the number of revolutions per spot joint, with maximum heat input obtained of 11 kJ at the number of revolutions of 500. The temperature measurement during FSSW showed agreement with the heat input dependence on the number of revolution. However, at the same revolutions of 500, it was found that the higher rotation speed of 1500 rpm resulted in higher temperature of 583 °C compared to 535 °C at rotation speed of 1000 rpm. This implies the significant effect for the rotation speed in the increase of temperature. The macro investigations of the friction stir spot-welded joints transverse sections showed sound joints at the different investigated parameters with significant joint ligament between the steel and brass. FSSW of steel/brass joints with a number of revolutions ranging between 250 to 500 revolutions per spot at appropriate tool speed range (1000â1500 rpm) produces joints with high load-carrying capacity from 4 kN to 7.5 kN. The hardness showed an increase in the carbon steel (lower sheet) with maximum of 248 HV and an increase of brass hardness at mixed interface between brass and steel with significant reduction in the stir zone hardness. Microstructural investigation of the joint zone showed mechanical mixing between steel and brass with the steel extruded from the lower sheet into the upper brass sheet.
Highlights
In 1991, friction stir welding (FSW) was initially introduced by TWI in the UnitedKingdom as a newly developed solid-state welding process, for joining aluminum alloys with specific requirements that should be fulfilled [1,2]
Many friction stir spot welding (FSSW) conditions were examined to explore the effect of the different parameters on developing high-quality dissimilar lap joints between brass (CuZn40) and lowcarbon steel (St 44-2)
At longer dwell time and higher number of rotations (500 R), the heat input was at a maximum, which provided a better condition for stirring the steel beneath the tool pin, leading to a clear increase of the hardness values reaching its maximum (262 HV), as shown in Figure 11 for steel in the middle zone
Summary
Kingdom as a newly developed solid-state welding process, for joining aluminum alloys with specific requirements that should be fulfilled [1,2]. Friction stir spot welding (FSSW) was developed as one of its variant for local joining of similar and dissimilar sheets [3,4,5,6,7,8,9] as a promising technique with similarities to the basic concepts of linear FSW with a specific requirement where no lateral movement of the tool is required [10]. The stir zone or nugget in the friction processed materials characterized by fine, dynamic, recrystallized microstructures due the severe plastic deformation experienced at high temperatures [11,12,13,14]. The steels comprising mixture structures of ferrite and martensite are termed dual-phase (DP) steel
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