Subsequent enhancement of mechanical properties using heat treatment of steel/copper bimetallic structures manufactured by laser powder bed fusion

The steel/copper bimetallic structures inherit both the excellent thermal/electrical conductivity of copper alloys and the mechanical strength of steel, making it valuable for applications in heat exchangers, injection molds and the power industry. Laser powder bed fusion (LPBF) is a promising manufacturing method for the fabrication of steel/copper bimetallic structures, but the inhomogeneous heterogeneous interfaces still need to be subsequently processed to further enhance their mechanical properties. In this investigation, an attempt was made to optimize the interfacial microstructure of steel/copper bimetallic structures fabricated by the LPBF process through annealing treatment to improve their interfacial strength. As a result, the annealing treatment increased the interfacial bonding strength of the steel/copper bimetallic structure by 28% and without reducing the elongation. This is attributed to the elemental homogenization and internal stress release during heat treatment, as well as the mechanically interlocked structure of fine crystals embedded in coarse crystals formed by Cu/Fe interdiffusion at the boundary of the steel/fusion zone. However, no significant phase transitions were identified in the heterogeneous interface. A suitable heat treatment process can diffusely distribute the Cu/Fe immiscible phase and maintain fine grains. This work discusses in detail the microstructure evolution under different annealing treatments as well as the underlying mechanisms for the improvement of mechanical properties, providing a simple and effective method for post-treatment reinforcing the heterogeneous interface of 316L/CuSn10 bimetallic structure fabricated by LPBF.