A comparative study on the employment of heat treatment, electric pulse processing and friction stir processing to enhance mechanical properties of cold-spray-additive-manufactured copper

The relatively weak interfacial bond and brittleness of cold sprayed deposits limit their industrial applications for the fabrication of complex structural components. In this study, pure copper, as a typical material for cold spray additive manufacturing (CSAM), was deposited and then post-processed with conventional heat treatment (HT) and newly developed electric pulse processing (EPP) and friction stir processing (FSP), in order to improve the microstructure and mechanical properties of the deposits. The results show that EPP, FSP, and HT can heal the weak interfaces between deposited particles, with EPP and FSP being considerably better than HT. Recrystallized fine grains and elongated grains at the interfacial regions transformed into coarser grains after EPP and HT. FSP refinement affects the grains of the whole deposit and completely rearranges the topology of the deposited particles. Mechanical tests reveal that an ultimate tensile strength of 310 MPa and elongation of 40% were reached after FSP, while the ultimate tensile strength of 209 MPa and elongation of 19% were reached with EPP. The main strengthening mechanisms of the EPP deposit are the improved bonding at the interfaces and the high angle grain boundaries and twins. For the FSP deposit, the improved interface bonding, the superfine grains along with the strain hardening effect are the main strengthening mechanisms.