# An Analysis of Mechanical Properties for Ultrasonically Welded Multiple C1220-Al1050 Layers
## 3 Results of the Experiment  
### Evaluation of Mechanical Joint Performance  
The specific value examined in this study is the shear strength. Two types of specimens were used to measure the shear strength, and the data obtained from each specimen are as follows. (1) Maximum tensile strength measurement using a test method that tensions the entire multi-layer welding specimen. (2) Shear strength measurement of three welds by tensioning each weld zone. A 10 ton UTM (Universal Testing Machine) was used to measure the shear strength, and to measure the maximum tensile strength, cover plates were inserted between the base materials, as shown in Figure 4, so that the load was transferred horizontally to measure the precise shear strength. Figure 5 shows the experimental procedure for measuring the multi-step shear strength of the weld. To measure the shear strength of each weld, the experiments were conducted in a sequence: Al-Cu tensile test, Cu-Al tensile test, and Al-Cu tensile test. Since there are no standards for measuring the shear strength of ultrasonic welds, a comparison of the welding conditions was performed by forming welds of the same area and measuring the quantitative shear strength.  
The shear strength measurement test results using a UTM are divided into three types through the displacement-load curve. As shown in Figure 6, three interfaces are created when ultrasonic welding with four sheets, and their characteristics are as follows. Three ultrasonic welds are used to weld the four thin plates.  
Figure 4: Procedure of one-step shear strength test for multi-lap joint welding.  
Figure 5: Procedure of multi-step shear strength test.  
Weld zone 1 in Figure 6 is bonded together with the aluminum and copper surface, and the indentation of the horn reduces the sectional area of the aluminum weld. The fracture location in weld zone 1 is divided into an interface fracture and an indentation fracture, and it has the form of an aluminum fracture because the strength of aluminum is weaker than that of copper. For weld zone 2, the fracture is located at the center of the weld in the form of a joint between the upper copper plate and the lower aluminum plate. It also shows the same interface fracture or aluminum fracture as weld zone 1. Weld zone 3 is the same as weld zone 2. The aluminum plate that exists in both weld zone 2 and 3 bears the form of a base material fracture when weld zone 2 and 3 are stably bonded.  
The shape of the welded specimen is shown Figure 7a. At the cross section in Figure 7b, the bond line was not observed due to the characteristics of solid phase bonding. When resistance welding, the bond line is observed but both heat affected zone and bonding line are not observed, since ultrasonic metal welding is one of the plastic-flow welding methods [26; 27]. However, it was confirmed that two metals were closely bonded to each other after observing the weldment under 3000 times magnification, as shown Figure 7c.  
Figure 6: Three zones of the ultrasonic weldment of multi-layer, dissimilar materials Al and Cu.  
Figure 7: Cross-section ultrasonic weld zone with amplitude 70%, welding time 2.5 sec, and pressure load 3 bar: (**a**) cross-sectional cutting position; (**b**) joint cross section (x40); (**c**) joint cross section (x3000).