# Research on a Low Melting Point Al-Si-Cu (Ni) Filler Metal for 6063 Aluminum Alloy Brazing
## 3 Results and Discussion
### Wettability of Al-Si-Cu (Ni) Filter Metal on Substrates  
The fluidity of the filler metal was one of the factors affecting the quality of brazed joints, and the spreading area of the brazing alloy on the base material can well reflect the wetting and flowing joint-filling ability of brazing filler metal. The effects of different Cu and Ni contents on the spreading properties of the Al-Si-Cu and Ni filler metals are shown in Table 4. The spreading area per unit mass of Al-Si-(10, 15, 20) Cu filler metals increased from 0.58 cm\({}^{2}\) to 2.87 cm\({}^{2}\). Compared with the Al-6.5 Si-20 Cu filler metal, the spreading area per unit mass of Al-6.5 Si-20 Cu-(1.0, 1.5, 2.0) Ni filler metals increased by 12.5%, 8.0%, and 6.8%, respectively. When 2.0 wt.% Ni was added, the liquidus temperature of the filler metal increased, the melting range became wider, and the spreading ability decreased,  
Figure 6: EDS element mapping of microstructures of the (**a**) Al-6.5 Si-20 Cu and (**b**) Al-6.5 Si-20 Cu-1.5 Ni filler metals.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Testing Points** & **Al** & **Si** & **Cu** & **Ni** \\ \hline A & 1.05 & 98.88 & 0.06 & 0 \\ B & 42.20 & 0.23 & 57.57 & 0 \\ C & 96.41 & 0.21 & 3.38 & 0 \\ D & 41.63 & 0.06 & 57.18 & 0.82 \\ E & 95.87 & 0.47 & 3.34 & 0.31 \\ F & 37.47 & 0.12 & 52.64 & 9.78 \\ G & 1.06 & 98.26 & 0.31 & 0.38 \\ \hline \hline \end{tabular}
\end{table}
Table 3: EDS results on the chemical composition (wt.%) of points marked in Figure 6.  
which may be due to the formation of more complex alloy compounds between Ni and Al, which affected the fluidity of the filler metal [21; 22; 23].  
Figure 7 shows the microstructures of the spreading interface of the Al-6.5 Si-20 Cu/base material and the Al-6.5 Si-20 Cu-1.5 Ni/base material. According to [PERSON]'s law of diffusion, there was a large concentration difference between the filler metal and the base metal; therefore, Cu in the filler metal diffused into the base metal along the grain boundaries and reacted with Al in the base material to form \(\theta\)(Al\({}_{2}\)Cu) intermetallic compounds. The base materials interlaced with each other at the spreading interface, forming a diffusion layer between the filler metal and the base material. The microstructures of the spreading interface in Figure 7c,d were analyzed by EDS, and the results are shown in Table 5 and Figure 8. Table 5 shows that the microstructure of the Al-6.5 Si-20 Cu filler metal/Al spreading interface was mainly composed of three phases: the \(\alpha\)-Al phase, a \(\theta\) (Al\({}_{2}\)Cu) phase, and a Si phase. Figure 8 shows that Ni replaced a certain amount of Cu in the microstructure of the Al-6.5 Si-20 Cu-1.5 Ni filler metal/Al spreading interface such that the Cu and Ni are interlaced, which weakened the influence of Cu on the brittleness of the brazed alloys. Therefore, the addition of Ni can not only advance the interdiffusion of elements between the filler metal and the base metal, but also refine the grains and improve the performance of the filler metal.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Filler Metals** & **Spread Area per Unit Mass (cm2/g)** \\ \hline Al-6.5 Si-10 Cu & 0.58 \\ Al-6.5 Si-15 Cu & 1.71 \\ Al-6.5 Si-20 Cu & 2.87 \\ Al-6.5 Si-20 Cu-1.0 Ni & 3.28 \\ Al-6.5 Si-20 Cu-1.5 Ni & 3.12 \\ Al-6.5 Si-20 Cu-2.0 Ni & 3.08 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Analysis of the spreading properties of the filler metals.  
Figure 7: Microstructures of the spreading interface of the Al-6.5 Si-20 Cu (**a**,**c**) and Al-6.5 Si-20 Cu-1.5 Ni (**b**,**d**) filler metal.