High-toughness joining of aluminum alloy 5754 and DQSK steel using hybrid clinching–welding process

Abstract

The spot clinching–welding process proposed in this work involves mechanical clinching and resistance spot welding phases. A 1.5-mm-thick aluminum alloy 5754 sheet was joined with a 0.8-mm-thick drawing-quality special-killed (DQSK) steel sheet by forming a mechanical–metallurgical hybrid joint. The interfacial microstructures were examined using scanning electron microscopy, and digital image correlation was used to analyze the mechanical behavior of the Al/steel dissimilar joints during tensile–shear testing. The load-bearing ability of the Al/steel dissimilar joint was improved by using the spot clinching–welding process because of both mechanical and metallurgical factors: (1) the large faying area between the die and workpiece improved the uniformity of the temperature distribution of the liquid nugget, leading to a thinner and smoother Al–Fe intermetallic compound (IMC) layer in the AA5754/DQSK bonding area, and (2) the structural feature of the Al/steel clinching–welding joint prevented the main strain zone from crossing the Al–Fe IMC layer during the tensile–shear test, leading the crack-propagation path to turn from the Al/steel interface to the fusion zone on the AA5754 side. Those two factors resulted in large-scale deformation of the Al/steel joint during the fracture process and, consequently, high energy absorption.