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Ultrasonic Effect on the Mechanical Behavior of Metals

Kang, Thomas Wonjune
http://rave.ohiolink.edu/etdc/view?acc_num=osu1713547372652399

Abstract Details

2024, Master of Science, Ohio State University, Welding Engineering.
Ultrasonic vibration has widely been studied for potential in the metal forming industry for its ability to temporarily soften the material. The lack of understanding of the underlying mechanisms of ultrasonic softening and difficulty in scaling to industrial applications has limited its use. To better understand the fundamentals to the softening mechanism, ultrasonic-assisted (UA) micro-tensile tests of low-carbon steel, aluminum alloy 2219 varying grain size, and titanium grades 2 & 5 are conducted in this study. The ultrasonic vibration is oriented along the tensile axis, and the ultrasonic amplitude is uniform in micro-dogbone specimen. Acoustic softening is observed, increasing with ultrasonic amplitude for all materials. Further investigation on the unique residual effect after ultrasonic treatment based on the microstructure is conducted. Low-carbon steel exhibited residual softening increasing with ultrasonic amplitude. EBSD analysis was conducted on the steel samples strained to 10% strain to explain the reduction of strain hardening during UA and residual softening after UA. Two ultrasonic amplitude levels were compared along with a control NoUA case. Higher LAGB fractions were observed with increasing ultrasonic amplitude, attributed to enhanced dislocation motion resulting in dipole annihilation and subgrain formation. Lower amplitudes assisted in lattice rotation with minor change in the microstructure while higher amplitudes resulted in significant intragranular deformation. Aluminum alloy 2219 was friction stir processed to achieve a refined microstructure and compared to a Al2219-T4 temper with a larger grain size. The resultant reduction of flow stress from ultrasound with varying grain size was similar, however, residual hardening was observed in the T4 temper, while no residual effect was observed in the refined microstructure. Also, the ultimate tensile stress and elongation improved after ultrasonic treatment in the T4-temper. With the aid of Digital-image-correlation (DIC), the ultrasonic effect on Lüders band in low-carbon steel and Portevin-Le Chatelier (PLC) in aluminum alloy 2219 was investigated. The Lüders band averaged a higher maximum strain rate with increasing ultrasonic amplitude. The PLC band frequency was enhanced and initiated with ultrasonic treatment, corresponding to enhanced band movement being a possible factor to the necking resistance seen experimentally. Titanium-6Al-4V (Grade 5) and pure titanium (Grade 2) are compared to investigate the difference of UA effect on a significantly strengthened alloy compared to its pure element. The reduction of flow stress was observed to be similar despite the difference in strengthening mechanisms and elongation between the two grades. The stress reduction magnitude in decreasing order given a certain ultrasonic amplitude is as follows: low-carbon steel, titanium grades, and aluminum 2219. The magnitude of reduction at a certain ultrasonic amplitude is similar within each material system. The residual response to ultrasonic treatment was found to differ based on the microstructure.
Xun Liu (Advisor)
Avraham Benatar (Committee Member)
71 p.
Materials Science; Mechanical Engineering
Deformation; titanium; aluminum steel; EBSD; tensile; formability; mechanical behavior; strength; ductility; digital image correlation; DIC; spatiotemporal; strain rate; subgrain; ultrasonic vibration; acoustic softening; acoustoplasticity; stress superposition; dislocation theory; residual softening; hardening; grain rotation; KAM; GROD; ferrite

Recommended Citations

Citations

  • Kang, T. W. (2024). Ultrasonic Effect on the Mechanical Behavior of Metals [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1713547372652399

    APA Style (7th edition)

  • Kang, Thomas. Ultrasonic Effect on the Mechanical Behavior of Metals. 2024. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1713547372652399.

    MLA Style (8th edition)

  • Kang, Thomas. "Ultrasonic Effect on the Mechanical Behavior of Metals." Master's thesis, Ohio State University, 2024. http://rave.ohiolink.edu/etdc/view?acc_num=osu1713547372652399

    Chicago Manual of Style (17th edition)

osu1713547372652399
92
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This open access ETD is published by The Ohio State University and OhioLINK.
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