Additive manufacturing of copper-tool steel dissimilar joining: Experimental characterization and thermal modeling

In high-pressure die casting applications, efficient cooling of the die/mold is critical to reduce cycle time. Tool steel such as H13 is widely adopted to make these components due to its excellent mechanical properties. However, the low thermal conductivity of tool steel largely impedes its cooling capability. Therefore, joining tool steel with copper to enhance the overall thermal conductivity is critical. In this study, pure copper was deposited on H13 substrates using a laser-aided additive manufacturing process. Depositing Cu on H13 directly and via interlayers of a nickel-based alloy Deloro 22 (D22) were employed. Both experimental characterization and computational analysis were conducted to study the properties of these structures. The results highlight the cracking failure in direct depositing copper on H13 while these cracks have been successfully eliminated when the D22 interlayers were introduced. Evidence of strong bonding at the Cu/D22 and D22/H13 interfaces was obtained. A sharp drop of hardness was observed over the Cu/H13 direct joint interface, while this descend was largely smoothed when D22 was inserted as interlayers. The directly joined Cu/H13 structure has a high longitudinal tensile residual stress (~385 MPa) at the Cu/H13 interface. By adding D22 interlayers, a reduced longitudinal tensile residual stress (~192 MPa) is obtained at the Cu/D22 interface. D22 interlayers have mitigated residual stress at the dissimilar joints.