Spark plasma welding joining of copper- AISI4140 steel: Microstructures and mechanical properties

The main aim of this research study was to characterize the microstructures and mechanical properties of Cu-AISI4140 steel solid-state joining created via the spark plasma welding (SPW) method with and without using molds. To explore the effect of mold on the joining of copper/steel, the SPW process was done at 650 °C for 30 min under the pressure of 20 MPa, with and without mold. Microstructural evaluations indicated the diffusion-affected zone (DAZ) in the SPW process increased with mold, as compared to the sample considered in the absence of the mold process. Also, the SPW process with the mold, in response to the lack of the formation of the oxide layer and dead zone, was affected by the process pressure, in comparison to that without the mold process, leading to the reduction of unjointed areas and the formation of micropores constrained at the joining interface; as such, the joining strength was increased from 42 MPa to 90 MPa. The elevation of the applied pressure from 20 MPa to 40 MPa at 650 °C resulted in enhancement of the joining strength up to 106 MPa, but it had no perceptible effect on raising the strength and diffusion affected zone (DAZ) of the joint.