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Joining Dissimilar Structural Alloys by Vaporizing Foil Actuator Welding: Process Conditions, Microstructure, Corrosion, and Strength

Liu, Bert C, Liu
http://rave.ohiolink.edu/etdc/view?acc_num=osu1471629967

Abstract Details

2016, Doctor of Philosophy, Ohio State University, Materials Science and Engineering.
The continual push for vehicle weight reduction has called for the incorporation of non-conventional automotive alloys, such as advanced high-strength steels, aluminum alloys, and even magnesium alloys and titanium alloys. The advent of these new alloys calls for new joining technologies. Resistance Spot Welding and Arc Welding have served the automotive industry well in joining steel components. However, because these are fusion-based processes involving high heat, they are not suitable for joining combinations of dissimilar metals or high-performance alloys. Thus the search continues for a technique capable of joining the said metals effectively, economically, and flexibly. The work featured in this dissertation aims to explore and develop Vaporizing Foil Actuator Welding (VFAW) as a promising technique for dissimilar-metal joining. VFAW is a form of solid-state impact welding that was developed in the Ohio State University in 2011. In this work, some 20 dissimilar-metal combinations of industrially relevant structural alloys were screened for weldability by VFAW. Successful welds were obtained for some 10 combinations, many of which were Al/Fe pairs, which are a most popular material pair for automotive weight reduction. Various aspects of VFAW were explored according to the axiom of Materials Science: process, microstructure, and property. First, the VFAW process was characterized by grooved target plates and photonic Doppler velocimetry (PDV). The former characterized the angle of impact and the latter, the speed of impact, where the speed and angle of impact are the critical process parameters of impact welding. Using these tools, optimal welding parameters were obtained for select material pairs. Second, the microstructure of the weld was studied by metallography. The best weld bonds were associated with continuous direct metal-metal interfaces with little or no voids or intermediate phases such as intermetallic compounds (IMCs). In addition, impact welding often gave rise to wavy bond interfaces, which provided mechanical interlocking, and grain refinement, which provided extra strengthening. Signs of ductile failure and material transfer on the fracture surface were evidence of strong, tough bonds. Third, the properties of the weld were evaluated by mechanical testing. In tensile lap-shear testing and peel testing, failure often occurred in a base metal at near its native strength, showing that the weld was even stronger than one of the base metals and that very little mechanical knock-down was brought on by the welding process. Corrosion behavior was studied by salt-spray corrosion testing, and 5 coated Al/Fe pairs retained >80% strength through a 30-day long exposure. Throughout this work, the VFAW technique itself was also developed and expanded. The foil actuator, which is the heart of the process, was refined to deliver more even, consistent pressure. Weldability was improved by means of modified welding configurations, such as vacuum, interlayers, and venting holes. Spot welds were miniaturized by 50% while maintaining mechanical performance. Flyers up to 2 mm thick were welded successfully. With such a unique set of capabilities described above, VFAW has great potential to be a competitive technology for dissimilar joining and a significant enabler for vehicle weight reduction.
Glenn Daehn (Advisor)
Michael Mills (Committee Member)
Stephen Niezgoda (Committee Member)
235 p.
Engineering; Materials Science
Dissimilar metal joining, vehicle weight reduction, galvanic corrosion, solid-state welding, impact welding, vaporizing foil actuator welding, structural alloys

Recommended Citations

Citations

  • Liu, Liu, B. C. (2016). Joining Dissimilar Structural Alloys by Vaporizing Foil Actuator Welding: Process Conditions, Microstructure, Corrosion, and Strength [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1471629967

    APA Style (7th edition)

  • Liu, Liu, Bert. Joining Dissimilar Structural Alloys by Vaporizing Foil Actuator Welding: Process Conditions, Microstructure, Corrosion, and Strength. 2016. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1471629967.

    MLA Style (8th edition)

  • Liu, Liu, Bert. "Joining Dissimilar Structural Alloys by Vaporizing Foil Actuator Welding: Process Conditions, Microstructure, Corrosion, and Strength." Doctoral dissertation, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1471629967

    Chicago Manual of Style (17th edition)

osu1471629967
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This open access ETD is published by The Ohio State University and OhioLINK.