Based on the changes of microhardness, tensile strength, and impact resistance caused by the difference of macroscopic morphology and microstructure of welded joints, this paper studied the effect of different ultrasonic power on the properties of welded joints during the welding of homogeneous armor steel. It is experimentally found that the macroscopic morphology of those joints is very different. Compared with conventional welding, ultrasonic welding can increase the weld depth and the width of the heat-affected zone (HAZ) on either side of the weld. However, only the ultrasonic wave at an appropriate power level can increase the weld width. In addition, appropriate ultrasonic power can significantly improve the grain state of the weld. With the increase of ultrasonic power, the grain size in HAZ will decrease. The microhardness of the weld will first increase and then decrease, while the microhardness of the HAZ will increase. This is basically consistent with the changing trend of impact resistance. An ultrasonic wave can also increase the tensile strength of a welded joint up to 802 MPa, 12.4% higher than that in conventional welding. However, a high-power ultrasonic wave will bring down the tensile strength. This study provides guidance for the selection of ultrasonic-assisted regulation power to achieve the different properties of homogeneous armor steel joints.

The injection of ultrasonic wave into a melt during casting can refine grain size, improve grain distribution, and thereby enhance casting performance. The available studies on ultrasonic-assisted casting are mostly about inserting a transducer directly into the melt. Such a method is not suitable for sand casting. Therefore, the study of ultrasonic sand casting by indirectly injecting ultrasonic waves into an aluminum alloy melt through a sand mold was proposed and carried out in this study. The effects of ultrasonic waves of different powers at different solidification stages on the microstructure and mechanical properties of the melt were studied. Compared to conventional sand casting, the samples prepared by ultrasonic sand casting have finer grains and better grain distribution, as well as higher mechanical properties. Moreover, the sample’s performance improves to different levels when the same ultrasonic wave is injected at different periods, when compared to the injection of ultrasonic waves with different powers in the same period.

The welding performance and defects of thick aluminum alloy plates with medium and high strength are always a hot research topic. In this study, ultrasonic technology was used to regulate the properties and defects of welded joints of a 7A52 aluminum alloy plate during double-sided welding, and these welded joints were compared with conventional welded joints. X rays were used to macroscopically detect the defects of welded joints. An optical microscope was used to analyze the grain structure and microdefects in each zone of welded joints. The tensile and impact tests were carried out on the joints. The fracture morphology of tensile and impact specimens was observed using a scanning electron microscope, and the defects and slag inclusions were analyzed by energy dispersive spectroscopy. In the process of ultrasonic welding, the crystallization process of the molten metal pool was changed, and the solidification and heat transfer environment under ultrasonic influence directly led to the change in the properties and defects of welded joints. The experimental results show that the 7A52 aluminum alloy joints can produce deep penetration and very few macroscopic defects after ultrasonic adjustment. Ultrasonic waves can refine the grains in the weld zone, heat-affected zone, and fusion zone and reduce the microdefects in each zone. The tensile and impact properties of ultrasonic welds have been improved by 84% and 87%, respectively. Therefore, ultrasonic waves can regulate the welding performance and defects of 7A52 aluminum alloy plates and other aluminum alloy plates with a similar structural composition. This study provides guidance for the selection of a double-sided welding method with low cost, high efficiency, and good joint performance for aluminum alloy plates.

By applying ultrasonic treatment to ZL205A aluminum alloy melt containing different Cd contents and then using a tensile test, a scanning electron microscope experiment, and a metallographic experiment, the influence of ultrasonic treatment to ZL205A aluminum alloy melt on the properties of aluminum–copper alloy with different Cd contents in the liquid phase high-temperature region was studied. The effect of ultrasonic treatment on the solidification structure of ZL205A aluminum alloy was investigated. The results showed that there was no significant difference in the form of Cd and the solid solution rate of the aluminum alloy with different Cd contents in ultrasonic-assisted casting. However, the effect of ultrasonic waves on the high-temperature liquid phase of the melt of ZL205A aluminum alloy can effectively reduce the porosity defects in the solidification structure of the casting, refine the solidification structure, and make the structure more uniform. The ultrasonic cavitation effect can promote the formation and uniform distribution of Al–3Ti and improve the nucleation rate, and the effect can continue after heat treatment. This can solve the problem that increasing Cd content in ZL205A greatly reduces the toughness of castings while increasing the strength. The sample with a Cd content of 0.20% and with ultrasonic treatment has the highest strength, the average tensile strength is 475.5 MPa, and the yield strength is 381.75 MPa. However, compared with the conventional casting samples with the same Cd content, the decrease in elongation was significantly reduced.

To solve the problems of large deformation and poor welding quality commonly observed during the double-sided welding of Q355 thin plates, this study systematically investigated the effects of single-sided ultrasonic-assisted welding on the weld formation, microstructure, mechanical properties, and residual stresses of the plates, and compared this welding process with conventional ones. Experimental results indicate that ultrasonic assistance is associated with improved weld shape and quality, contributing to a flatter weld surface and more symmetric cross-sectional profile. In contrast to conventional welds, welds produced by single-sided ultrasonic-assisted gas metal arc welding show no obvious oxide inclusions and a reduced tendency for columnar grain growth. In a single tensile test for each welding condition, the measured tensile strength was 552 MPa for conventional welding and 575 MPa for single-sided ultrasonic-assisted gas metal arc welding. These tensile results should be interpreted as indicative trends and require replication to assess scatter and statistical significance. Furthermore, single-sided ultrasonic-assisted gas metal arc welding is associated with lower welding residual stresses, with peak stress values reduced by up to 36.23% along the longitudinal path. This technique provides an engineering reference for improving weld-quality consistency during the double-sided welding of Q355 thin plates without altering the welding specifications.