Effect of Ni in Zn-22Al filler metal on the microstructure and mechanical properties of Cu/Al brazing joints
Aims:To study the the influence of Ni on the melting characteristics and spreading performance of Zn-Al cored welding wire.Methods:Add Ni powder to the brazing flux to complete Ni in-situ alloying in Cu/Al joints during the brazing process.Then analyze the effects of the different Ni contents addition on the properties and microstructure of Cu/Al dissimilar alloy joints brazed with Zn-22Al brazing material.Results:Ni addition significantly enhanced the spreadability of Zn-22Al filler metal on Al substrate and the tensile strength of joints used for Cu/Al brazing.The spreadability of brazing materials is improved by 26.75％when Ni addition amount is 5％,and the tensile strength of Cu/Al brazed joint also increased by 61.79％when Ni addition amount reached 7％.Conclusions:Ni powder addition effectively improved the microstructure of the Zn-22Al seam,leading to the refinement of the primary phase,the reduction of Zn-rich boundary phase,the formation of lamellar eutectoid microstructure between primary grains,as well as the thickness of brittle intermetallic compounds layer formed on the Cu side.All these microstructure changes contribute to the improvement of Cu/Al joint strength.
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