Researches On Brazing Fillers For Intermediate Temperature Brazing Cemented Carbide YG16 And 45 Steel

WC decomposition and an η phase appear in the high temperature welding of a cemented carbide and steel,Ag-Cu-based intermediate temperature brazing fillers in the market have a high Ag content and contain environmentally-unfriendly elements comprising Cd,Pd and the like,and the processability and the mechanical performances of a post-welded joint are worsened after adding melting point decrease elements comprising Sn,In and the like,so the composition of an Ag-Cu-based Cd-and-Pd-free intermediate temperature brazing fillers is designed in order to research on intermediate temperature brazing cemented carbide YG16 and 45 steel.An Ag-Cu-Sn-Zn-Ni brazing filler alloy foils is made through a rapid solidification technology,some performances and microstructures of the brazing filler alloy are analyzed,the rule of the influences of the alloy element Zn on the performances of the brazing filler is researched,the brazing filler is used in the intermediate temperature brazing of YG16/45steel,the phase composition and the microstructure of a brazed joint and the influences of the content of the alloy element Zn on the microstructure and mechanical performances of the joint are analyzed,and results show that:The Ag-Cu-Sn-Ni brazing filler is composed of an(Ag)phase of FCC,a(Cu)phase of FCC and a Cu13.7Sn phase,a Cu0.64Zn0.36 phase partially precipitates after the addition of the Zn element,and with the increase of the Zn content,the melting point of the brazing filler decreases,the tensile strength of the brazing filler firstly rises and then decreases,the rate of elongation decreases,and the formality decreases.The structure of the rapidly-solidified solid brazing fillers is an extremely-fine irregular eutectic structure,and a fine chrysanthemum unit cell structure is formed when a small amount of Zn is added;when the Zn content is 2.5wt%,unit cells have a minimum dimension and appear as microcrystalline chrysanthemum unit cells;and when the Zn content continuously increases,a netted(Ag)phase and a(Cu)phase distributed in the netted(Ag)phase are formed,irregular and uniform large solid solution phases of(Ag)and(Cu)increase,and the tensile strength of the brazing filler decreases from a maximum value;and with the increase of the Zn content,a solid/liquid phase line greatly decreases,the spacing of the solid/liquid phase line slightly increases,and the alloy foil has an average tensile strength of above 500MPa,an average elongation of 13.4%.The designed Ag-Cu-Sn-Zn-Ni brazing fillers can satisfy requirements of the intermediate temperature brazing of the cemented carbide and steel,and is used in the brazing of the YG16/45 steel to obtain a joint structure mainly comprising a spatially-netted(Cu)phase,a spatially-netted(Ag)phase and a small amount of Cu-Sn and Cu-Zn phases,and there is a certain metallurgical reaction between the brazing fillers and a base metal.With the increase of the content of Zn in the brazing fillers,a fusion line of the brazing fillers and the interface of the base metal becomes clearer,an interface primary phase(Cu)changes from disorderly dispersed distribution to the distribution of growing along a heat dissipation direction,island-shaped(Cu)phases in a brazed seam reduce in quantity and increase in dimension,and the(Ag+Cu)lamellar eutectic spacing decreases.When the Zn content is 12wt%,the(Cu)phase grows up abnormally,so the mechanical performances decrease.The Ag42Cu38Sn10Zn9Ni1 composition brazing filler has a Ts value of 577℃,a TL value of 613℃ and a ΔT value of 36℃,and has the characteristics of uniformly distributed brazinged seam microstructure,and realization of the shear strength of the brazed joint reaching 321MPa.