# An Analysis of Mechanical Properties for Ultrasonically Welded Multiple C1220-Al1050 Layers
## 3 Results of the Experiment
### The Optimization of Welding Conditions
#### 3.2.2 Comparison of the Welding Quality  
Additional experiments were carried out to evaluate the performance of weld zone under optimum conditions. The non-optimizing welding conditions for the comparison with the optimized welding conditions were selected by the highest welding strength among the 25 tests performed previously. Non optimizing welding conditions, such as 50% of amplitude, 3.5 sec of welding time, and 1.0 of pressure load were used. The experimental method was divided into two parts; first, the maximum strength was compared when both the aluminum plate and the copper plate were simultaneously tensioned. In addition, three shear strength measurement tests were performed for each specimen to determine the strength of the welds individually. Figure 14 shows the displacement-strength curve when all of the welding specimens were tensioned using optimized welding conditions and non-optimized experiment conditions. Both welding conditions exhibited similar displacement-strength curves. The maximum tensile strength was confirmed to be 45% higher under optimized welding conditions compared to other cases. The maximum tensile strength refers to the load which the two sheets of aluminum can withstand. This is represented by the load applied to the entire material, when the four plates are overlapping. This refers to the force before the fracture of the first aluminum indentation. Afterwards, the second aluminum plate withstands all tensile loads, causing the aluminum base material to fracture. The fracture occurs due to the plastic deformation of the second aluminum, and the section where the load is maintained consistently during the constant displacement is the section where the second aluminum is deformed.  
Figure 15 is a graph measuring the shear load of each weld zone. Through identifying the strength of each weld, it was found that when the optimal conditions are not used, the weldability decreased as the distance of the weld from the horn increased, and the distribution of the strength levels becomes very large. However, when the optimal conditions were used, the strength was reduced in the  
Figure 14: Comparison strength between non-optimized and optimized conditions.  
aluminum base material directly in contact with the mixed material, but the strength was improved for weld zones 2 and 3. Weld zone 1 showed a reduction in strength of about 36%, but weld zone 2 showed a strength improvement of 32%, while weld zone 3 showed a strength improvement of 110%. As an amplitude rate of 80% was used, that was considered to be a result of the decrease in the thickness of the indentation as the depth of the indentation on the surface becomes deeper. Figure 16 shows the thickness of the aluminum weld according to the depth of the indentation. The depth of the indentation was 270 \(\upmu\)m when the optimal welding conditions were used, and was about 80 \(\upmu\)m thinner under normal welding conditions. As the amplitude increased, the size of the indentation of aluminum surface increased and the bonding strength of the weldment increased, but that had the effect of reducing the thickness of occured the indentation. In addition, as shown in Figure 16, since the fracture position in the weld 1 at the aluminum indentation, the reduction of the indentation thickness was directly related to the strength reduction. Nevertheless, the strength of welds 2 and 3 was improved. That has the effect of improving the overall strength of the welded part.  
Figure 16: Comparison of cross section for aluminum indentation thickness between optimal welding conditions and non-optimal welding conditions. (**a**) Optimal welding conditions; (**b**) non-optimal welding conditions.  
Figure 15: Comparison of strength between non-optimized conditions and optimized conditions at each weld zone.