Explosive Coating of Ag–Cu Filler Alloy on Metal Substrates and Its Effect on Subsequent Brazing Process

Abstract

An austenitic stainless steel plate was coated with a sheet of Ag-Cu filler alloy by using explosive energy to simplify the subsequent brazing operation. The coated specimen had a typically wavy interface, and there were no defects like void. The adhesion at the interface was retained even after heating at a temperature of more than eutectic point of the Ag-Cu binary system (1 052 K), although the molten Ag-Cu alloy did not show a good wettability on the stainless steel without coating. To investigate the effect of the coating on the interfacial microstructure and the bonding strength of finally obtainable joints, two coated specimens were overlapped and then heated at 1 173 K for 0.3 ks in a low vacuum. The obtained joint had a shear strength of about 200 MPa, and broke mainly within the Ag-Cu alloy after a shear test. The joint brazed with the Ag-Cu alloy was also fabricated under the same heating conditions. Its shear strength was about 90 MPa, and the fracture position was at the Ag-Cu alloy/stainless steel interface. This indicates that the substantial bond between the Ag-Cu alloy and the stainless steel, which is achieved by explosive energy, contributes to the subsequent brazing process. Additionally, a commercially pure Ti plate was used as a substrate. In this case, the advantages of the coating process could not be recognized in the finally obtained joint. It is found that the substantial bond provided by explosive energy is canceled by the formation of a reaction layer on the brazing operation.