Cu is a fundamental material for a large variety of industries including electrical power system and electronic industry. Laser processing of pure Cu is challenging because of Cu’s very low absorptivity to most laser beams, and this difficulty is applicable to the recently developed laser powder bed fusion (LPBF) additive manufacturing (AM) as well. How to realize high-quality LPBF forming is urgently pursued in order to maximize its advanced manufacturing potential in directly making various Cu parts.

In this thesis, theoretical analysis of laser absorptivity was given. Based on the analysis, three possible routes to enhance the laser absorptivity of highly reflectivity materials were proposed, i.e., powder alloying, powder surface modification and using short-wavelength laser. Accordi...[ Read more ]

Cu is a fundamental material for a large variety of industries including electrical power system and electronic industry. Laser processing of pure Cu is challenging because of Cu’s very low absorptivity to most laser beams, and this difficulty is applicable to the recently developed laser powder bed fusion (LPBF) additive manufacturing (AM) as well. How to realize high-quality LPBF forming is urgently pursued in order to maximize its advanced manufacturing potential in directly making various Cu parts.

In this thesis, theoretical analysis of laser absorptivity was given. Based on the analysis, three possible routes to enhance the laser absorptivity of highly reflectivity materials were proposed, i.e., powder alloying, powder surface modification and using short-wavelength laser. According to the first two routes, selective laser melting (SLM) of Cu-10Sn-0.4P pre-alloyed powder and surface-oxidized powder was conducted respectively. Residual stress of the as-printed Cu-10Sn-0.4P was measured and relieved via heat treatment. Microstructure and mechanical properties were investigated, too, according to which the effect of trace amount of P element was confirmed. During the SLM of surface-oxidized Cu powder, laser remelting was adopted to counter the high thermal conductivity of Cu and provide extra liquid phase for better densification. Various research means were used to investigate mechanical performances, microstructural details, and electrical performance of the as-printed Cu. Furthermore, femtosecond laser was used to modify the surface of the SLM-manufactured Cu-10Sn-0.4P. The laser-modified samples exhibited an increased microhardness, and their surface wettability and optical properties were also changed due to the laser-induced periodic surface structure. Finally, several typical applications of laser-based 3D printing of Cu and Cu alloys such as jewelry, copper sheathing, heat exchanger and metamaterials were demonstrated, and the related properties such as density and surface roughness were characterized to verify the good printability of Cu and Cu alloys.