| The common filler metal for aluminum alloys was Al-Si alloy, however the brazing temperature with the Al-Si filler metals is close to the solidus temperature of most aluminum alloy which will lead to the base metal overburnt and the shape of Si phrase in Al-Si alloy is harmful to the performance of brazed joints. To solve these problems,Cu, Zn, La and Sc were added into Al-4Si alloy. 9 different components of Cu, Zn and La had been added into Al-4Si filler metals by orthogonal design and Al-4Si-15Cu-35Zn-0.05 Sc, Al-4Si-15Cu-35Zn-0.1Sc and Al-4Si-15Cu-35Zn-0.2Sc were designed by replacing La to Sc from Al-4Si-15Cu-35Zn-0.2La,Al-4Si-15Cu-35Zn-0.2La-0.1Sc was designed by added both of Sc and La into Al-4Si-15Cu-35 Zn. The effect of Cu, Zn, La, Sc to the melting temperature,spreadability of Al-4Si alloy and the fracture morphology, shear strength of brazed joints had been studied by optical microscope, XRD, SEM and differential scanning calorimetry. The main conclusions in this thesis have been summarized as follows:Compare the micro-structures of Al-4Si-x Cu-y Zn-z La(x=10, 15, 20; y=20, 30, 35;z=0.1, 0.2, 0.5), the results showed the phases of the filler metals didn’t change when the contents of Cu, Zn changed, but the amount of Al2Cu(θ) increased with the increasing of Cu. The main phases of Al-4Si-x Cu-y Zn-z La filler metal were α-Al, Si,Al2Cu(θ), and La-rich phase is found in the filler metal when La≥0.2%. The dimension of the primary Si orthogonal test results showed La and Zn had stronger effect on the dimension of the primary Si than Cu. Compare filler metal No.6 and filler metal No.10-No.15, it showed that Al-4Si-15Cu-35Zn-0.2La-0.1Sc had the smallest size of Si phrase and also showed the metamorphism mechanism of La,Sc is occurred in Si phase growth process.The orthogonal results also showed that La and Cu had a stronger effect on melting point than Zn and Al-4Si-20Cu-35Zn-0.5La filler metal had the lowest melting point which is 464℃. The addition of Sc didn’t have a strong effect on melting point of filler metals but it can reduce the solid-liquid phase interval of filler metal and Al-4Si-20Cu-30Zn-0.1La-0.2Sc had the narrowest range of solid-liquid phase which is19℃. Similarly, Orthogonal test results of spreadiability of 1-9 group filler metal showed La and Cu had a stronger effects on spreadability than Zn. Compare the effection of La, Sc on spreadiability of filler metals, the results showed add both La andSc into filler metal had the strongest effection on spreadiability which the maximum area was 252.58mm2.Brazing LF6 with Al-4Si-15Cu-35 Zn-0.2Al-0.1Sc under different temperature with different holding time, the results showed that when the brazing temperature is constant, the shear strength increased with the longer holding time; when the holding time is constant, the shear strength also increased with higher brazing temperature.The failure morphology showed a mixed ductile and brittle fracture feature which didn’t change by the holding time. The largest average shear strength of brazing joints had been got under 530℃ holding 15 mins which is 116.14 MPa. |
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