Abstract
With the growing need to develop light weight structures joining dissimilar metals is inevitable. Hence a fundamental understanding of the microstructure evolution and bond formation mechanism is necessary. In this work we probe the welded interface in aluminum and steel joined using vaporizing foil actuator welding (VFAW) a novel impact welding process. The goal of such a detailed characterization campaign is to understand the bond formation mechanism. The study shows that the interfacial microstructure has a pronounced hierarchical nature. At the macro scale, the interface is characterized by a wavy interface which is a result of extensive plastic deformation that accompanies the process. Detailed transmission electron microscopy shows evidence for the formation of a liquid film at the interface resulting in significant inter diffusion of Fe. The solidified structure at the interface consisted of crystalline α-Al and an amorphous metastable Al-Fe intermetallic compound similar to the observations in rapid solidification of Al-Fe alloys. The sub-nm scale characterization of the interface using atom probe tomography showed two distinct zones 1. A magnesium (5 at.%) and oxygen (15 at.%) rich (not detectable using energy dispersive spectroscopy) which was probably from the decomposition of the surface oxide film 2. The rapidly solidified reaction zone consisting of primary crystalline α-Al and an amorphous Al-Fe (15 at.%)-O (0.5 at.%)-Si (1.5 at.%). Based on these observations a mechanism for the bond formation is presented.
Original language | English |
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Pages (from-to) | 119-128 |
Number of pages | 10 |
Journal | Materials Characterization |
Volume | 151 |
DOIs | |
State | Published - May 2019 |
Funding
The work at The Ohio State University was supported by the Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technology Office under award number DE-0007813. Taeseon Lee acknowledges the National Science Foundation GOALI program and the Civil, Mechanical and Manufacturing Innovation Division – Award Number CMMI-1537471. APT was conducted at ORNL's Center for Nanophase Materials Sciences (CNMS), which is a U.S. DOE Office of Science User Facility. This research was performed, in part, using instrumentation (FEI Talos F200X STEM) provided by the Department of Energy, Office of Nuclear Energy, Fuel Cycle R&D Program and the Nuclear Science User Facilities.