Hierarchical Morphology and Formation Mechanism of Collision Surface of Al/Steel Dissimilar Lap Joints via Electromagnetic Pulse Welding

Puquan Wang,Yunqi Yan,Bo Feng,Xianquan Jiang,Xinwei She,He Peng,Yang Ran,Dongyang Li,Daolun Chen

doi:10.3390/met11091468

Abstract

The aim of this study was to characterize detailed microstructural changes and bonding characteristics and identify the formation mechanism of collision surface of Al6061–Q355 steel dissimilar welded joints via electromagnetic pulse welding (EMPW). The collision surface was observed to consist of five zones from the center to the outside. The central non-weld zone exhibited a concave and convex morphology. The welding-affected zone mainly included melting features and porous structures, representing a porous joining. The secondary weld zone presented an obvious mechanical joining characterized by shear plateaus with stripes. The primary weld zone characterized by dimples with cavity features suggested the formation of diffusion or metallurgical bonding. The impact-affected zone denoted an invalid interfacial bonding due to discontinuous spot impact. During EMPW, the impact energy and pressure affected the changes of normal velocity and tangential velocity, and in turn, influenced the interfacial deformation behavior and bonding characteristics, including the formation of micropores which continued to grow into homogeneous or uneven porous structures via cavitation, surface tension, and depressurization, along with the effect of trapped air.

Highlights

Steel sheets were used in the electromagnetic pulse welding (EMPW) tests, with their chemical compositions listed in Tables 1 and 2
The Al and steel sheets of 1 mm in thickness were machined into coupons of dimensions of 20 mm × 100 mm, with the length being parallel to the rolling direction
This rapid process eventually leads to the formation of a special collision rapid process eventually leads to the formation of a special collision surface with multiple surface with multiple zones, which are defined as impact-affected zone (I), primary zones, which are defined as impact-affected zone (I), primary weld zone (II), secondary weld zone (II), secondary weld zone (III), welding-affected zone (IV), and non-weld zone (V) from outside to the center

Summary

Introduction

Dissimilar joining of aluminum alloy and steel as a potential technique to manufacture lightweight, cost-effective, and environmentally friendly structures has been increasingly applied in the transportation industry [1,2,3,4,5]. It is difficult to obtain sound joints using conventional fusion welding techniques due to different melting temperatures (~660 ◦ C for Al and ~1538 ◦ C for steel), the severe segregation resulting from mutual dissolution at Al/steel interface, and the formation of brittle intermetallic compounds (IMCs), such as FeAl3 , Fe2 Al5 , FeAl2 , FeAl, etc. The induced impact energy along with a proper collision angle leads to severe plastic deformation at the interface, causing the rupture of contacting surfaces and the material jetting and removal, resulting in a deformed and rough fresh surface

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Discussion

Conclusion