Effect of powder size in microwave joining of oxygen-free copper to SS304

This paper investigates the prospect of microwave hybrid heating to join oxygen-free copper with stainless steel (SS304). The effect of size of copper (Cu) powder interlayer in the microstructure and mechanical properties of the joint formed is investigated, along with the incites on the mechanism of joint formation. Cu powder of average sizes 4 and 45 μm was studied. The microwave heating rate was observed to be high for 4 μm Cu in the absence of voids or porosities in the joint region. Voids were observed in the interlayer when 45 μm Cu powder was used. The joint was formed due to volumetric diffusion of the major elements of the substrates, e.g. Fe, Cu, Cr that was verified by energy dispersive spectroscopy. Oxides were present for 45 μm Cu which was absent for 4 μm Cu. X-ray diffraction and energy-dispersive X-ray spectroscopy analysis concluded that no intermetallic compound was formed along the interlayer. The micro-hardness of ∼128 HV was observed to be uniform across the interlayer depicting a good metallurgical joint. The maximum tensile shear strength of 83.12 MPa was recorded for 4 μm copper powder and microwave time of 14 min, exhibiting ductile failure of the joint.