Study On The Embrittlement Mechanism And Performance Optimization Of Flux-cored Zn-Al Filler Metal

Flux-cored Zn-A1filler metal is commonly used in Cu-Al connection due to itsadvantages such as high joints strength, good corrosion resistance, reliable inperformance. Unfortunately, the aging degradation behavior of Zn-Al filler metal in hot,humid and high pressure environment during storage affects the brazing technology. Atpresent, embrittlement theories about Zn-Al filler metal is rarely reported both indomestic and international research, and its embrittlement mechanism is unclear. In thispaper, embrittlement behavior of flux-cored Zn98-Al filler metal and Zn85-Al fillermetal in hot and humid environment were studied. Accelerated corrosion test wasutilized to simulate the hygrothermal atmospheric corrosion conditions.“Embrittlementphenomenon” of filler metal and the influence of different heat treatment process on themicrostructures and properties of flux-cored Zn-A1filler metal were investigated. Theembrittlement mechanism and methods to avoid “embrittlement phenomenon” were alsodiscussed.The results indicated that the reason for the “embrittlement phenomenon” ofZn98-Al filler metal was mainly intergranular corrosion, when corrosion reach a certainextent, corrosion crack and corrosion holes were formed. With the increase of corrodingtime, corroding depth increased linearly. Intergranular corrosion is electrochemicalcorrosion, of which the intragranular zinc-rich η phase was as the cathode, thealuminum-rich α phase in the grain boundary was as the anode. Additionally,inhomogeneity of microstructure and the presence of stress accelerated the intergranularcorrosion of the flux-cored Zn-Al filler metal.The modification of KBF4and homogenization treatment on flux-cored Zn-A1filler metal was beneficial to the homogeneity and stability of microstructure, whichenhanced the spreadability on pure aluminium surface and corrosion resistance.Ductility and toughness of flux-cored Zn-A1filler metal was improved significantly.The stress relief annealing eliminated the residual stress from cold and hot processingand reduced the effects of stress on promoting corrosion, thereby improved the corrosionresistance of the Zn-A1filler metal. The Zn-Al filler metal corrosion resistance sensitiveto the annealing temperature is higher than annealing time. The optimal annealingprocess parameters of corrosion resistance was250℃annealing temperature and2hannealing time.In summary, the aging "embrittlement phenomenon" of flux-cored Zn-A1filler metal was the result of electrochemical corrosion. The the following measures shoud betaken to avoid “embrittlement phenomenon” of Zn-A1filler metal: the modification ofKBF4, increasing relief annealing process, vacuum packaging.