A new approach to joining of bulk copper using microwave energy

Metallurgical joining of high thermal conductivity materials like copper has been technically challenging. This paper illustrates a novel method for joining of bulk metallic materials through microwave heating. Joining of copper in bulk form has been carried out using microwave energy in a multimode applicator at 2.45 GHz and 900 W. Charcoal was used as susceptor material to facilitate microwave hybrid heating (MHH). Copper in coin and plate forms have been successfully joined through microwave heating within 900 s of exposure time. A sandwich layer of copper powder with approximately 0.5 mm thickness was introduced between the two candidate surfaces. Near complete melting of the powder particles in the sandwich layer does take place during the microwave exposure leading to metallurgical bonding of the bulk surfaces. Characterisation of the joints has been carried out through microstructure study, elemental analysis, phase analysis, microhardness survey, porosity measurement and tensile strength testing. X-ray diffraction (XRD) pattern indicates that some copper powder particles got transformed into copper oxides. XRD analysis also reveals that the dominant orientation (3 1 1) in starting copper powder got transformed into a preferential orientation (1 1 1) in the joint. A dense uniform microstructure with good metallurgical bonds between the sandwich layer and the interface was obtained. The hardness of the joint area was observed to be 78 ± 7 Hv, while the porosity in the joint was observed to be 1.92%. Strength character of the copper joints shows approximately 29.21% elongation with an average ultimate tensile strength of 164.4 MPa.

Research highlights
► Joining of bulk copper with a sandwich layer using 2.45 GHz microwaves at 900 W.
► Melting of sandwich layer and metallurgical bonding with bulk surfaces.
► Mechanism of joining using microwave hybrid heating is explained.
► Tensile strength and elongation of microwave induced joints are monitored.
► Failure mechanisms of microwave induced joints are studied.