Abstract Crack detection in welded structures of dissimilar material using guided waves is not well developed. This paper scrutinizes the effect of material discontinuity in plate structures and the excessive plastic deformation, within friction stir welded (FSW) joints, on the propagation behavior of guided waves toward their application in weld assessment. Quantifying the scattering, attenuation and group velocities of the guided waves when they propagate across different media, as well as determining the elastic properties of the material within the weld will provide rich information about the behavior of ultrasonic waves. Three pristine defect free friction stir welded plates were used in this study. The first specimen was a weld of dissimilar materials aluminum/magnesium alloy (AA6061-T6/AZ31B), the second was of dissimilar aluminum alloy grades (AA6060/AA7020-T651), and the third was of the same aluminum grade (AA7020-T651/AA7020-T651). The elastic properties across all the welds were extrapolated using nano-indentation technique. Ultrasonic guided waves were excited and measured using piezoelectric wafers and laser Doppler vibrometer (LDV). Additionally, a sensor network design was implemented on the three specimens using piezoelectric transducers. Wave reflections, based on the LDV results and the information collected from the sensor network, were observed at the weld zone of the AA6061-T6/AZ31B FSW plate, while no reflections were detected at the weld zones in the AA7020-T651/AA7020-T651 and AA6060/AA7020-T651 plates. The results were correlated with the measurements obtained from the nano-indentation experiment, where a sharp change in the elastic properties of the base metals in the AA6061-T6/AZ31B welded joint were detected, unlike the other two plates that showed constant elastic properties across the weld zones. The results showed that the amount of scattering at the joints is a function of the wave propagation direction. It was noticed that the average wave reflection generated when the wave crossed from the AZ31B to the AA6061-T6 base metal was around 35% of the incident signal, but it reduced to 25% when the wave propagation direction was reversed. Characterizing ultrasonic waves in FSWs and the behavior of the incident and reflected waves in the welded zones will further improve on the technology used for inspection and monitoring of solid state welded joints.

中文翻译：

---

超声波在相似和异种摩擦搅拌焊接接头检测中的应用

摘要 使用导波对异种材料焊接结构的裂纹检测还没有得到很好的发展。本文详细研究了板结构中的材料不连续性和搅拌摩擦焊 (FSW) 接头内的过度塑性变形对导波在焊接评估中的应用的传播行为的影响。量化导波在不同介质中传播时的散射、衰减和群速度，以及确定焊缝内材料的弹性特性，将提供有关超声波行为的丰富信息。本研究中使用了三种原始无缺陷搅拌摩擦焊板。第一个试样是异种材料铝/镁合金（AA6061-T6/AZ31B）的焊缝，第二个是不同的铝合金牌号（AA6060/AA7020-T651），第三个是相同的铝牌号（AA7020-T651/AA7020-T651）。使用纳米压痕技术外推所有焊缝的弹性性能。使用压电晶片和激光多普勒测振仪 (LDV) 激发和测量超声波导波。此外，还使用压电换能器在三个样本上实施了传感器网络设计。根据 LDV 结果和从传感器网络收集的信息，在 AA6061-T6/AZ31B FSW 板的焊接区观察到波反射，而在 AA7020-T651/AA7020-的焊接区未检测到反射。 T651和AA6060/AA7020-T651板。结果与从纳米压痕实验中获得的测量结果相关联，其中检测到 AA6061-T6/AZ31B 焊接接头中母材的弹性性能发生急剧变化，这与其他两块板不同，后者在整个焊接区显示出恒定的弹性性能。结果表明，接头处的散射量是波传播方向的函数。注意到当波从 AZ31B 穿过 AA6061-T6 基体金属时产生的平均波反射约为入射信号的 35%，但当波传播方向反转时，它减少到 25%。表征 FSW 中的超声波以及焊接区域中入射波和反射波的行为将进一步改进用于检测和监测固态焊接接头的技术。