Selective laser melting of copper alloys

Abstract

In this project, copper alloys were studied to ascertain their suitability for the selective laser melting (SLM) process. Copper’s inherently high electrical and thermal conductivity makes it attractive for the fabrication of components which require these properties such as thin plate heat exchangers and conformal cooling channels.

The copper alloy, C18400, is a CuCrZr alloy with especially high electrical and thermal conductivity[1]. Different processing parameters were attempted for the C18400 SLM process and the highest relative density of the finished component of 94.6% were obtained at a laser power of 400 W, scan speed of 300 mm/s, hatch spacing of 0.12 mm and layer thickness of 0.03 mm. The samples were subjected to a 2 stage heat treatment process to determine if mechanical properties improved. Samples age hardened for 5 hours were found to have the highest microhardness value, 65.6HV0.3. Field Emission Scanning Electron Microscope (FESEM) images were analysed and it was observed that there was precipitation along the dendritic structure along with clear grain boundaries and differing grain orientation. Due to the significant level of porosity found in the samples, further tensile strength and thermal conductivity tests were not carried out.

K220 is a copper-nickel-silicium alloy with addition of chromium[2]. This alloy was chosen for experimentation as it is able to produce high relative component densities when used for SLM processes [3]. In this experiment, a high relative density of 99.9% was obtained during SLM. K220 was similarly subjected to a 2 stage heat treatment process to determine if mechanical properties improved. It was found that age hardening of 12 hours gave maximum hardness in the XY plane while maximum hardness in the YZ plane was obtained after 25 hours. The highest ultimate tensile strength (UTS) was achieved with 12 hour age hardening.