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An Overview
Published in J. David, N. Cheeke, Fundamentals and Applications of Ultrasonic Waves, 2017
This was one of the first areas of ultrasonics to be developed, but it has remained poorly developed theoretically. It involves many heavy-duty industrial applications, and often the approach is semi-empirical. Much of the early work was carried out by Wood and Loomis, who developed a high-frequency, high-power system and then used it for many applications. One of the problems in the early work was the efficient coupling of acoustic energy into the medium, which limited the available power levels. A solution was found with the exponential horn; a crude model was developed by Wood and Loomis, and this was perfected by Mason using an exponential taper in 1950. The prestressed ceramic sandwich transducers also were important in raising the acoustic power level. Another problem, which led in part to the same limitation, was cavitation. Once cavitation occurs at the transducer or horn surface, the transfer of acoustic energy is drastically reduced due to the acoustic impedance mismatch introduced by the air. However, work on cavitation gradually led to it becoming an important subject in its own right. Ramification of the process led to operations such as drilling, cutting, and ultrasonic cleaners. Other applications of cavitation included sonochemistry and sonoluminescence. High-power ultrasonics also turned out to be a useful way to supply large amounts of heat, leading to ultrasonic soldering and welding of metals and plastics.
A novel approach to dissimilar joining of AA7075 to AZ31B by friction stir soldering using Sn intermediate layer
Published in Materials and Manufacturing Processes, 2022
Omid Karimi-Dermani, Alireza Abbasi, Ghasem Azimi Roeen, Mohammad Javad Nayyeri
Two practical methods were proposed for controlling the establishment of Al-Mg intermetallics at the weld nugget. One of them is to apply an intermediate layer between the parent substrates, and the other is to reduce the maximum temperature of the Al-Mg interface to a temperature below the Al-Mg eutectic temperature (437 ͦ C) by the use of processes with lower heat input or by cooling in special environments with high cooling power.[30–32] Mofid et al.[31] found that it is possible to restrict the formation of such intermetallics by underwater friction stir welding. Zn foils were utilized by Niu et al.[32] as an intermediate layer to modify the characteristics of friction stir-welded AZ31-7075 connections. They reported that the Zn interlayer was able to influence the geometry and mechanical and microstructure features of the joints. A wider stir zone was achieved in the presence of the Zn interlayer, and the shear strength of the connection was enhanced by the formation of less-brittle Zn-Mg intermetallics instead of high-brittle Al-Mg intermetallics. Karimi et al.[17] utilized Sn foils as an interlayer for connection of AA7075 to AZ31B through friction stir welding. Although formation of Al-Mg intermetallics could not be prevented by applying a Sn intermediate layer, shear strength of Al/Mg dissimilar joints was improved by using a Sn interlayer as a result of lubricating impacts of melted tin. Also, it is shown that Al-Mg intermetallic compounds could be avoided through forming Mg2Sn intermetallic compounds in the ultrasonic soldering of Mg to Al alloys with a Sn interlayer.[33–35] The advantage of ultrasonic soldering over friction stir welding is having more control over interface temperature and negligible mixing of dissimilar materials. Thus, the probability of Mg-Al formation is much lower in ultrasonic soldering compared with friction stir welding.