Study On Filler Metal, Flux And Technology For Stepped Brazing Of 6063 Aluminum Alloy

The aluminum and its alloys are widely used as a kind of structural materials, especially the aluminum alloy 6063 is very popular due to its good properties of formability, mechanism weldability and corrosion resistance. The chassis of radar transmitter, receiver and signal processing are manufactured with 6063 in the world. In order to light the weight and improve the reliability, the stepped brazing process is required to braze the radar chassis because of the complicated structure. In this paper, brazing alloys as well as the matched fluxes, which are suitable for brazing 6063 in high and medium temperature with shielding gas furnace, are studied. In the meantime, parameters of brazing process are optimized.The effect of contents on the melting points, spreading property and shear strength of Al-Si-Cu-Ni-RE is researched by changing the level of Si,Cu,Ni,RE according to orthogonal test method. The microstructure of brazing metal is analyzed with SEM and EDS. The results show that the spreading area is dominated by the composition of filler metal and brazing temperature; The black brittle phaseθ(Cu Al2) and macrosegregation flocculent phase decrease the performance of the joint, while the matrix phaseα(Al) with face-centered cubic solid solution and Si phase with conglobulation feature make the performance of the joint better; Cu is the main factor that influences the melting points of the filler metal, next is Ni, Si and RE. The melting points of filler metal sharply lows as the Cu content increases.CsF-AlF₃ and KF-AlF₃ series fluxes are selected to research the effect of the fluxes on removing the oxide film of aluminum alloy 6063 at varied temperature. The reaction mechanism of flux with surface oxide film of aluminum alloy 6063 was analyzed and discussed. The results show that reaction and solution are the mechanism of CsF-AlF₃ removing surface oxide film from Al-alloy 6063 and the HF generated from NH4F at high temperature is the key compound. Moreover, the presence or formation of H2O accelerates the generation of HF, which accelerates the Striping rate of oxide film accordingly. No CsF and AlF₃ except a little of CsAlF4 was found in the reaction product of CsF-AlF₃ flux. The main product of KF-AlF₃ flux is KAlF4 at 570℃and a small amount of KMgF3 but no KAlF4 at 610℃. The results also indicates that Mg, Mn and KAlF4 will be gradually consumed at 610℃, which lead to sharp increasing of melting point and worse flowing property of the flux..The effect of brazing parameters on the hardness, strength, microstructure, and corrosion resistance of 6063 brazing joint is studied. The results show that with high temperature flux, the brazing metal spreads well above the heating rate of 15℃/min, but with intermediate flux, requires for heating rate will be higher than high temperature flux. Micro hardness of three kinds of brazing joints with different treatment is tested. Results indicate that Micro hardness of brazing joint after aging is the highest, of which hardness of the brazing seam and base metal is almost equal. Hardness of brazing seam and its diffusion area of brazing joint after solution is obviously higher than base metal's. Hardness of brazing seam after brazing is higher than base metal's, either. Shear strength of three kinds of brazing joints at different brazing temperature is tested. The results show that shear strength of brazing joint at 560℃is the highest, which decreases with brazing temperature. Effect of heating rate and holding time on microstructure of brazing joint is analyzed. Conclusion indicates that CuAl2 dendrites distribute unevenly at slow heating rate and Si grain becomes coarse but CuAl2 dendrites don't change significantly after long holding time.Effect of contents of Si, Cu, Ni and RE on the corrosion potential, weight loss and corrosion rate of Al-Si-Cu-Ni-RE is studied by changing the level of Si, Cu, Ni and RE according to orthogonal test method. The microstructure is observed with SEM and EDS before and after corrosion test. The results show that the corrosion potential is corresponding to weight loss, the weight loss increased with the decrease of corrosion potential. Ni is the dominant factor that influences corrosion rate, followed by Si, Cu, RE. Cl- is the main reason of inducing brazing metal to pit. Pitting occurred on local area of brazing metal which has obviously reticulate pattern intercrytalline corrosion.