1. Introduction
2. Materials Used and Experimental Method
2.1 Materials used
2.2 Experimental method
2.2.1 Single-mode laser welding
3. Experiment Results and Discussion
3.1 Microstructure and solidification cracking behavior in Cu-Al5052 single-mode fiber laser welds
Fig. 2

3.2 Investigation of the effect of Ni on solidification cracking behavior by calculating the weld solidification temperature range
Table 3
Table 4
Cooling rate [K/s] | 10000 |
---|---|
Solidification completion ratio [%] | 99 |
Secondary dendrite arm spacing [m] | 0.000001 |
Fig. 5

Fig. 6

Table 5
4. Conclusions
1) The weld zone with inhibited pores was secured under all conditions through Cu-Al laser penetration welding. The occurrence of solidification cracking was confirmed regardless of Ni-P coating application, but the crack position was slightly different. While Al and Cu were scattered across the entire area of diluted fusion zone (FZ) at specific ratios in the case of uncoated Cu welds, solidification cracking was concentrated in Ni- and P-rich areas where the coating layer elements (Ni and P) were introduced into FZ in the case of Ni-P coated Cu welds.
2) Since the inflow of a considerable amount of coating layer elements was confirmed at the solidification cracking positions in Ni-P coated Cu welds, the effects of the coating layer elements on solidification cracking sensitivity, i.e., the weld solidification temperature range, were investigated. In the diffusion-control-type Scheil model calculation results using Thermo-Calc, the mushy zone increased for Ni coating compared to the uncoated Cu weld. In the actual quantitative analysis results, a high Ni content and a wide mushy zone of up to 1,060 K were also confirmed from compositions near the solidification cracking area.
3) P, one of the coating elements, was also identified as an element that extends the solidification temperature range during solidification with the Cu element. Therefore, it was judged that the solidification cracking sensitivity of Cu-Al5052 dissimilar welds increases during Ni-P coating, and solidification cracking is concentrated at positions where the direct inflow of the coating layer occurs.
4) In conclusion, the solidification cracking behavior of the weld zone can be exacerbated by the specific elements of the coating material and the resulting mixed composition in the bead of Cu-Al5052 dissimilar welds. Therefore, it is necessary to select the optimal coating material and coating layer thickness.