| It could not ensure to make a reliable copper-aluminum joint when brazing with traditional Zn98 Al filler metal because of the hard controlling of the interfacial reaction.However,this problem may be solved via fluxed-cored Zn98 Al filler metal.The purpose of this paper concentrated on the influence of fluxed-cored Zn98 Al filler metal on copper-aluminum joint.In this paper,copper and aluminum was brazed with fluxed-cored Zn98 Al filler metal and traditional Zn98 Al filler metal.The effect of flux addition method on the microstructure,chemical composition and corrosion resistance of the copper-aluminum joint was investigated of the copper-aluminum joint was investigated.The corrosion mechanism of copper-aluminum joint was studied.Results indicated that the usage of fluxed-cored Zn98 Al filler metal could reduce the brazing time and flux,and it's wettability on the base metals was superior to that of traditional Zn98 Al filler metal.The microstructure in the copper-aluminum joint brazed with fluxed-cored Zn98 Al filler metal consisted of ?-Zn phase?Zn-bearing CuAl2 phase and Cu-bearing Zn-Al eutectic phase.While ?-Al phase appeared except for phases abovementioned when brazing with traditional Zn98 Al filler metal.Because of the inhomogeneous distribution of hard copper-aluminum intermetallic compounds,the hardness of interface near Al side was lower than that near Cu side.The difference in the amount of copper-aluminum intermetallic compounds resulted in higher hardness in the copper-aluminum joint brazed with fluxed-cored Zn98 Al filler metal than that of traditional Zn98 Al filler metalThe polarization phenomenon did not happen during corrosion.Al dissolution generated in the Zn-Al eutectic phase and?-Al phase.The usage of fluxed-cored Zn98 Al filler metal could improve the corrosion resistance of copper-aluminum joints due to the reduction of the amount of phases susceptive to corrosion,comparing with traditional fluxed-cored Zn98 Al filler metal.Crack was generated at Al/filler metal interface while there was no crack at Cu/filler metal interface.Al dissolution resulted in numerous microviods and considerable lattice distortion stress,which could promote the crack nucleation.Crack nucleation always happened at the boundary of Zn-Al eutectic phase,at which corrosion attack initiate.Then crack extended by this boundary or toward inside Zn-Al eutectic phase,which depended on the most active grain boundary near the crack source.The shear strength of the Cu-Al joint brazed with flux-cored filler metal could reach 34.5MPa after immersing in 3.5wt%NaCl solution for 18 days,which is higher than that of the joint brazed with traditional Zn-Al filler metal. |
PDF Full Text Request