Exploring the Formation Mechanism of Aluminum/Steel Resistance Spot Welding Joint Assisted by Ultrasonic Vibration
In order to improve the quality of aluminum/steel spot welded joints,ultrasonic longitudinal vibration is introduced into the conventional resistance spot welding(RSW)process.Considering joint microstructure analysis,welding process energy analysis,and the results of finite element numerical calculations,the nugget formation mechanism of ultrasonic vibration-assisted resistance spot welding(UA-RSW)of aluminum/steel welded joint is determined.Subsequently,a comprehensive analysis of interfacial compounds,welding defects,microhardness,and joint strength characteristics during UA-RSW of aluminum/steel joints is conducted.The results demonstrate a significant reduction in the sizes of the aluminum/steel double nugget after the introduction of ultrasonic vibration.This reduction is a result of competing of multiple ultrasonic effects,where ultrasonic vibrations reduce the contact resistance between sheets.Additionally,the electrical of molten steel and thermal conductivities of molten aluminum increase due to acoustic cavitation and acoustic flow effects.Moreover,ultrasonic vibration increases the bulge height of the steel sheet,promotes the radial creep of molten aluminum and near-molten aluminum,expanding the effective bonding area between aluminum and steel sheets.Ultrasonic vibration also effectively reduces the thickness of the intermetallic compound(IMC)layer to less than 3.0 μm in thickness and inhibits the formation of interface welding defects.Tensile-shear tests demonstrate that ultrasonic longitudinal vibration can achieve an aluminum button pull-out failure mode,increasing its peak tensile-shear load by 48.68％compared with the conventional RSW process.
ultrasonic vibrationresistance spot weldingaluminum/steelmicrostructureevolution of double nuggets
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