# Research on a Low Melting Point Al-Si-Cu (Ni) Filler Metal for 6063 Aluminum Alloy Brazing
## 4 Conclusions  
In this paper, a new low-melting-point Al-Si-Cu (Ni) filler metal was designed and prepared. The melting characteristics, microstructure, and spreading wettability of the filler metal were researched and the microstructure and mechanical properties of the joint brazed with 6063 aluminum alloy were studied. The conclusions can be summarized as follows:  
(1) The Al-Si-Cu filler metal was mainly composed of \(\alpha\)-Al solid solution, a \(\theta\)(Al\({}_{2}\)Cu) intermetallic compound, and bulk primary Si. With increasing Cu, the melting temperature of the Al-Si-Cu filler metal decreased, the melting interval became narrower, and the spreading performance improved. The melting range of the Al-6.5 Si-20 Cu filler metal was 521.4-533.4 \({}^{\circ}\)C, and the spreading area per unit mass was 2.87 cm\({}^{2}\).  
(2) The Al-Si-Cu-Ni filler metal was mainly composed of \(\alpha\)-Al solid solution, a \(\theta\)(Al\({}_{2}\)Cu) intermetallic compound, bulk primary Si, and a \(\delta\)(Al\({}_{3}\)Ni\({}_{2}\)) intermetallic compound. The addition of Ni not only narrowed the melting range of the Al-Si-Cu filler metal but also transformed the coarse, brittle Al\({}_{2}\)Cu phase from a bulk to a lamellar-type structure, and the structure was refined. With increasing Ni content, the spreading ability of the Al-Si-Cu-Ni filler metal decreased. The melting ranges of the Al-Si-Cu-Ni solder were 8.6 \({}^{\circ}\)C, 7.7 \({}^{\circ}\)C,  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Points** & **Al** & **Si** & **Cu** & **Ni** & **Mg** \\ \hline A & 5.06 & 92.79 & 2.08 & 0 & 0.06 \\ B & 43.70 & 0.94 & 54.68 & 0 & 0.67 \\ C & 40.66 & 1.42 & 55.12 & 1.74 & 1.05 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Chemical composition (wt.%) of the points in Figure 13.  
Figure 13: Shear fractographs of the 6063 aluminum alloy joints brazed with (**a**) Al-Si-20 Cu, (**b**) Al-Si-20 Cu-1.0 Ni, (**c**) Al-Si-20 Cu-1.5 Ni, and (**d**) Al-Si-20 Cu-2.0 Ni filler metals.  
and 7.6 \({}^{\circ}\)C, and the spreading areas per unit mass were 3.28 cm\({}^{2}\), 3.12 cm\({}^{2}\), and 3.02 cm\({}^{2}\), respectively.  
(3) When Al-6.5 Si-20 Cu and Al-6.5 Si-20 Cu-(1.0, 1.5, 2.0) Ni filler metals were used to braeze 6063 aluminum alloy at 570 \({}^{\circ}\)C for 10 min, brazing joints with shear strengths of 117.2 MPa, 123.6 MPa, 136.3 MPa, and 150.4 MPa were obtained. Therefore, the addition of Ni can effectively increase the shear strength of the brazed joints.  
Conceptualization, C.P. and F.Z.; methodology, C.P. and F.Z.; software, C.P. and F.Z.; validation, C.P., F.Z., and X.D.; formal analysis, C.P. and F.Z.; investigation, D.Z. and K.L.; resources, M.W. and Y.T.; data curation, C.P. and X.D.; writing--original draft preparation, C.P.; writing--review and editing, C.P.; visualization, X.D.; supervision, D.Z. and K.L.; project administration, M.W. and Y.T.; funding acquisition, F.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the key special project of \"Science and Technology Boost Economy 2020\" of the Ministry of Science and Technology of China and the Science and Technology Program of Guizhou Province with Grant Nos. 20194106 and 20165654, 2021109.  
Not applicable.