Selective Laser Melting: On the Study of Microstructure of K220

Abstract

K220 copper parts were produced by Selective Laser Melting (SLM) technology. The relative densities and microstructures of the SLM parts under different laser energy densities were measured and analysed. We observed an increasing relative density when laser energy input was enlarged. However, when the laser energy density exceeded 700 J/mm3, severe balling occurred. In this work, a high relative density of 99.9% was obtained when an energy density of 200 J/mm3 was applied. The microstructure of the SLM parts revealed cellular dendrites with dimensions of 1 µm. Two different heat treatment processes were applied and the microstructure and micro-hardness were also investigated. Laminated precipitate with dimension of 1 µm can be seen after 25 hours of age-hardening. Moreover, when the age-hardeningperiod wasincreased from 12 hours to 25 hours, the micro-hardness improved from 187.9±5.2Hv0.1 to 192±11.2Hv0.1 inxy plane. This is due to precipitate hardening of K220 after the heat treatment process.