| Because of the excellent formability, good corrosion resistance and weldability, 3003 aluminum alloy, a kind of Al-Mn-rust aluminum, has been widely used in the aerospa ce, automotive, machinery and other fields. As a sophisticated and convenient connection method, brazing can make the workpiece occurs deformation as small as possible, playing an important role on the further application of aluminum. While the aluminum based filler metal has high melting temperature, application of aluminum alloy brazing is limited. Based on the Al-Si-Cu ternary solder, adding Zn elements can reduce the melting temperature of the solder, improve spreadability and strength of brazed joints. In this paper, nine kinds of filler metal with different components was designed and develoed by using the method of orthogonal experiment, and the impact of Cu, Zn and Si contents on the microstructures and properties of the filler metals were studied. According to the results of DSC analysis, spreadability experiment and microstructure analysis, the filler metal composition formul is optimized, developing Al-20Cu-10Zn-7.5Si(10#) filler metal. Al-25Cu-5Zn-7.5Si(7#) and Al-20Cu-10Zn-7.5Si(10#) was found that is the two kind of filler metal with optimal brazing characteristic, and selected to braze 3003 aluminum alloy. At last, the effects of brazing temperature and holding time on the microstructure and propertiy of the joints were discussed in this paper.Results showed that Cu and Zn elements impacted on the melting characteristics of filler metal greatest. Improving Cu and Zn content could decrease the liquidus and solidus temperature of filler metal, but opposite to that of element Cu, Zn element content was higher, the melting solder was higher. Within a certain range to improve the content of Cu, Zn and Si, spreading of filler metal was improved. The Al-Si-Cu-Zn filler metals consisted of four phases:α(Al) solid solution matrix, θ(Al2Cu) intermetallic compound distributed along the grain boundary, massive/acicular silicon phase dispersed in the matrix. When the Cu and Zn element content were high, grains of brittle θ(Al2Cu) phase and the Si phase became coarse, and the amount of eutectic structure declined significantly.Compared the joint of using Al-25Cu-5Zn-7.5Si(7#) with Al-20Cu-10Zn-7.5Si(10#), the result show Al-20Cu-10Zn-7.5Si(10#) is better for brazing 3003. The brazed joints consisted of center zone of brazed seam and diffusion zones on both the sides. The center zone of brazed seam consisted of α(Al) solid solution, θ(Al2Cu) intermetallic compound, silicon massive/acicular phase and fine Al Fe Mn Si phase. And diffusion zones consisted of α(Al) solid solution and element diffusion layers.When increasing the brazing temperature from 550 ℃ to 570 ℃ for 20 min or extending the holding time 10~40 min at 550 ℃ by using Al-20Cu-10Zn-7.5Si(10#) filler metal, the width of braze seam increased. On the other hand, grains of each phase in the center zone became coarse, where α(Al) solid solution area proportion increased significantly. In addition, the dentate α(Al) solid solution layer gradually thickened and the interface between the filler metal and the base metal was enhanced. As brazing temperature or holding time increased, the RT shear strength of the brazed joint increased gradually and then decreased. The RT shear strength can reach up to 70.8 MPa, about 53.3% of the 3003 aluminum alloy. The RT shear fracture of the joint occured at the interface between the α(Al), which exisited in both diffusion zone and center zone, and the brittle phase in the center zone of brazed seam. Intergranular brittle fracture was ductile brittle mixed fracture. Hardness of α(Al) solid solution increased from the base metal to the center zone. There were some porosity and slag defects in brazing seam inevitably. While Penetration and ablation defect can be effectively avoided by selecting the appropriate brazing process. |
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