RESEARCH AND DEVELOPMENT OF NEW FILLER MATERIALS FOR JOINING DIFFERENT MATERIALS BY ISOTHERMAL SOLIDIFICATION

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For the purpose of developing a new filler metal with lower melting point and giving higher bond-strength, several kind of filler metals made of Cu-X alloys and Cu-X-Y alloys (X : Mn or Ag, Y : Fe, Cr or Al) were produced and applied to brazing of a ductile cast iron (DCI) and a mild steel. Irrespective of the kind of filler metal, alloyed phases precipitated at the DCI side and grew toward the steel side by isothermal solidification. In case of using Cu-25% Mn filler metal, a DCI and a steel could be joined at lower temperature of 1223K, and the same bond-strength (about 300 MPa) as brazed with pure copper could be obtained when the DCI and steel was brazed at the temperature (1300 K) lowered by about 80K compared with the usual temperature of copper brazing. When the Cu-25% Mn filler metal was applied to brazing of a high chromium cast iron and a steel, alloyed phases precipitated and the bond-strength showed about 220 MPa. In case of brazing of a Ni-hard cast iron and a steel at 1300K, the bond-strength of about 300 MPa was obtained. The effects of addition of third element to Cu-25% Mn filler metal was observed. Based on the above results, it can be said that the Cu-25% Mn alloy is a promising filler metal with lower melting point for joining cast iron and steel.