Master of Science, The Ohio State University, 2022, Materials Science and Engineering

The process of laser impact welding utilizes impact welding and laser-driven flyers to form solid-state, metallurgical welds between similar or dissimilar metallic flyers and targets. With chemically augmented laser impact welding, stronger and thicker metal flyers and targets can be welded together. Using a high-powered laser, a laser pulse is shot through a transparent tamping layer onto a translucent layer of chemical liquid and the bare surface of a metallic flyer. The energy from the laser pulse detonates the chemical augment and the pressure created from the explosion is confined by the tamping layer. This pressure is directed towards the flyer that is then driven to velocities in the hundreds of meters per second within 20 microseconds. Under the correct conditions, high speed and acceptable impact angle between the flyer and target, jetting will occur. The jet cleans the surface of the flyer and target of oxides, and the two surfaces will form a solid-state, metallurgical bond. Using a chemical augment, thicker, stronger flyers and targets can be welded compared to unaugmented laser impact welding. With the chemical augment, a 3J, 8.1ns laser pulse can weld a 0.5mm Al2024-T3 flyer to a 0.5mm Al2024-T3 target. To explore the capabilities of chemically augmented laser impact welding, two chemical augments were used as candidates for the process. Various tamping materials and thicknesses were also investigated along with variance in the laser spot diameter. The velocities of flyers were measured using Photon Doppler Velocimetry and a thicker tamping layer produced higher velocities and larger deformations than thinner tamping layers did with the same parameters. The strength of the welds between 0.5mm Al2024-T3 flyers and targets were also measured using a tensile test. Over two-thirds of the welded samples failed by nugget pullout during these tensile tests, validating the strength of the welds formed. Micrographs of a welded sample were also collected to o (open full item for complete abstract)

Committee: Glenn Daehn (Advisor); Boyd Panton (Committee Member) Subjects: Engineering; Materials Science; Metallurgy

Doctor of Philosophy, The Ohio State University, 2020, Materials Science and Engineering

Driven by the need for global carbon footprint reduction, the automotive industries are increasingly focusing on lightweighting of vehicles. Use of multi-material combinations for body-in-white applications is one of the practical ways of accomplishing the broader goal of lightweighting. Over the past decade, the vehicular structure has seen progressive replacement of the more conventional low-carbon mild steels with a variety of advanced and ultrahigh-strength steels including Dual Phase (DP), high-strength low-alloy (HSLA) and boron, and also extensive integration of light metals, such as Al alloys. Development of strong, repeatable and dependable joints is crucial for the effective implementation of these multi-material combinations. Direct welding of disparate Al-steel combination is difficult to impossible through conventional fusion welding routes. Mechanical fastening and clinching techniques provide alternatives to fusion welding, however, there are stack-up feasibility limitations and addition of an externally exposed joining element adds weight and negates the larger goal of lightweighting as well as increases the susceptibility of the joint to galvanic corrosion. Solid-state welding technologies are good substitutes to fusion welding and mechanical fastening and clinching techniques and are currently being employed on a small scale in industries. Here, Vaporizing Foil Actuator Welding (VFAW), a variant of solid-state impact welding technique is being utilized to produce similar and dissimilar joints with materials relevant to the automotive industries. VFAW, a high-speed impact welding technique utilizes the very high pressures generated due to the rapid vaporization of a foil actuator to cause the impact of metal sheets to form nominally solid-state joints with little to no presence of heat affected zone, providing the process the ability to join a wide array of similar and dissimilar material pairs. The present study applies an adaptation of the V (open full item for complete abstract)

Committee: Glenn Daehn (Advisor); Antonio Ramirez (Committee Member); Boyd Panton (Committee Member) Subjects: Engineering; Experiments; Materials Science; Metallurgy

Master of Science, The Ohio State University, 2019, Materials Science and Engineering

Laser impact welding is a relatively new technology that combines the existing technologies of impact welding and laser-driven flyers to create solid state welds between a thin metallic flyer and a target. A high power laser pulse is fired through a transparent confinement layer and onto an ablative layer that is directly attached to the flyer. This ablative layer absorbs the laser energy and is vaporized creating a plasma that is in turn confined by the transparent confinement layer directing the pressure into the flyer. This drives the flyer to velocities of hundreds to thousands of meters per second in under a microsecond. When the flyer impacts the target if the velocity is high enough and the angle between the two is sufficient, the two surfaces of the materials will be cleaned of their oxides, which in turn allows for a solid-state metallurgical bond to be made between the flyer and target. By controlling the laser parameters, much thicker flyers than previously reported can be welded. Using a 24J 65ns pulse, a 305µm 3003Al flyer was welded to 6061-T6Al. These welds were extremely strong and failed through the 3003Al flyer in all cases when peeled. To further push laser impact welding towards a scalable industrial process, liquid backing layers such as water and glycerin solution were studied for their effect on flyer impact velocity. Impact velocity was measured using Photon Doppler Velocimetry and it was determined that while both are suitable for welding, water would be the preferred backing in an industrial application due to its ease of use and low cost. Potential applications of laser impact welding, such as beverage can manufacturing, are also outlined and discussed.

Committee: Glenn Daehn (Advisor); Xun Liu (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2016, 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 wel (open full item for complete abstract)

Committee: Glenn Daehn (Advisor); Michael Mills (Committee Member); Stephen Niezgoda (Committee Member) Subjects: Engineering; Materials Science

Doctor of Philosophy, The Ohio State University, 2015, Mechanical Engineering

Ultrasonic additive manufacturing (UAM) is a low temperature, solid-state manufacturing process that enables the creation of layered, solid metal structures with designed anisotropies and embedded materials. As a low temperature process, UAM enables the creation of active composites containing smart materials, components with embedded sensors, thermal management devices, and many others. The focus of this work is on the improvement and characterization of UAM aluminum structures, advancing the capabilities of ultrasonic joining into sheet geometries, and examination of dissimilar material joints using the technology. Optimized process parameters for Al 6061 were identified via a design of experiments study indicating a weld amplitude of 32.8 um and a weld speed of 200 in/min as optimal. Weld force and temperature were not significant within the levels studied. A methodology of creating large scale builds is proposed, including a prescribed random stacking sequence and overlap of 0.0035 in. (0.0889 mm) for foils to minimize voids and maximize mechanical strength. Utilization of heat treatments is shown to significantly increase mechanical properties of UAM builds, within 90% of bulk material. The applied loads during the UAM process were investigated to determine the stress fields and plastic deformation induced during the process. Modeling of the contact mechanics via Hertzian contact equations shows that significant stress is applied via sonotrode contact in the process. Contact modeling using finite element analysis (FEA), including plasticity, indicates that 5000 N normal loads result in plastic deformation in bulk aluminum foil, while at 3000 N no plastic deformation occurs. FEA studies on the applied loads during the process, specifically a 3000 N normal force and 2000 N shear force, show that high stresses and plastic deformation occur at the edges of a welded foil, and base of the UAM build. Microstructural investigations of heat treated foils confi (open full item for complete abstract)

Committee: Marcelo Dapino (Advisor); Amos Gilat (Committee Member); Blaine Lilly (Committee Member); Stephen Niezgoda (Committee Member) Subjects: Materials Science; Mechanical Engineering

Master of Science, The Ohio State University, 2008, Welding Engineering

Ultrasonic metal welding (UMW) is a solid-state joining process in which materials are held together under moderate forces while applying localized high frequency shear vibrations, creating a true metallurgical bond. While ultrasonics have been applied extensively to joining soft materials, such as copper and aluminum, applications for joining more advanced materials are limited. UMW has generally not been considered for more advanced materials due to poor tooling life and inadequate ultrasonic power levels. In a relatively short period of time, developments in UMW equipment and potential tool materials, may allow UMW to be applied to these more advanced metals. Using commercially-available ultrasonic spot welding equipment, the ultrasonic weldability of 304 and 410 stainless steel, commercially pure and 6Al-4V titanium, and Nickel-base superalloys 625 and 718 was investigated. Tool materials developed for friction-stir weld tooling were used to develop new ultrasonic tools. Tool textures and designs were also evaluated.

Committee: Karl Graff (Advisor) Subjects: