Systematic Review of Ultrasonic Impact Treatment Parameters on Residual Stresses of Welded Non-Sensitized Versus Sensitized Aluminum-Magnesium

Abstract : This thesis focuses on the use of x-ray diffraction to measure residual stresses around welds in 5XXX series aluminum-alloys used in naval ship structures both in the laboratory and the field. Tensile residual stresses are commonly generated during welding and, in sensitized alloys, can cause stress corrosion cracking. Peening techniques, such as ultrasonic impact treatment (UIT), can mitigate and possibly reverse these tensile residual stresses. This research uses x-ray diffraction to measure residual stresses around welds in AA5456 after UIT, around welds in AA5083 installed on-board a U.S. naval combatant and in AA5083 after in situ surface preparation. In the AA5456, we examined the importance of UIT parameters such as peening amplitude and pin size. It was found that all combinations of UIT parameters produced significant compressive stress but that some combinations resulted in extensive subsurface intergranular cracking in the sensitized AA5456. Optimal UIT parameters for mitigating the production of subsurface cracking were determined. In the AA5083, we examined the effect of field-based in situ surface preparation on residual stress measurements. The use of a portable x-ray diffractometry system to experimentally measure the distribution of residual stresses in aluminum-alloy ship structures on U.S. Navy vessels has been successfully demonstrated.