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Pure Copper (Cu) is very difficult to prepare using selective laser melting (SLM) technology. This work successfully prepared the pure Cu with high relative density and high strength by the SLM technology using a surface oxidation treatment. The gas-atomized pure Cu powder was used as the feedstock in this work. Before the SLM process, the pure Cu powder was initially handled using the surface oxidation treatment to coat the powder with an extremely thin layer of Cu2O. The SLMed highly dense specimens contain α-Cu and nano-Cu2O phases. A relationship between the processing parameters (laser power (LP), scanning speed (SS), and hatch space (HS)) and density of Cu alloy in SLM was also investigated. The microstructure of SLMed Cu consists of fine grains with grain sizes ranging from 0.5 to ~30 μm. Tensile testing and detailed microstructural characterization were performed on specimens in the as-SLMed and pure copper state specimens. The mechanical property experiments showed that the specimens prepared by SLM technology containing nano-oxide phases had higher yield strength and tensile strength than that of other SLM-built pure copper. However, the elongation was remarkably decreased compared to other SLM-built pure copper, due to the fine grains and the nano-oxides.

Samples of Al–Mg–Mn and Al–Mg–Mn–Er–Zr alloys were welded using the method of laser welding. The influence of Er and Zr on microstructure, microhardness and mechanical properties of the Al–Mg–Mn alloy welded joints were investigated. It has been found that addition of Er and Zr refines the grain size in the fusion zone, due to the formation of primary Al3Zr and Al3Er. Fine equiaxed grains are dominated near the fusion boundary of the Al–Mg–Mn–Er–Zr alloy joint, which is contrary with the columnar crystal in the Al–Mg–Mn alloy joint. Microhardness of the center of the fusion zone rises from 74HV0.1 to 84HV0.1 owing to the grain refinement by Er and Zr. The tensile test result shows that the ultimate tensile strength and yield strength are improved by adding Er and Zr. The main reason for this is related to grain refining strengthening.

In the present work, laser welding with filler wire was successfully applied to joining a new-type Al–Mg alloy. Welding parameters of laser power, welding speed and wire feed rate were carefully selected with the objective of producing a weld joint with the minimum weld bead width and the fusion zone area. Taguchi approach was used as a statistical design of experimental technique for optimizing the selected welding parameters. From the experimental results, it is found that the effect of welding parameters on the welding quality decreased in the order of welding speed, wire feed rate, and laser power. The optimal combination of welding parameters is the laser power of 2.4 kW, welding speed of 3 m/min and the wire feed rate of 2 m/min. Verification experiments have also been conducted to validate the optimized parameters.

Samples of Al-Mg-Mn-Zr-Er alloys were welded by the method of TIG welding. Microstructures of base metal and welded zones were analyzed by optical microscopy (OM), electron probe micro-analyzer (EPMA) and transmission electron microscopy (TEM). Particular emphasis was laid on the existence form of Er and its effect on the microstructure and the phase composition of the fusion zone. Results reveal that the trace rare earth element Er mainly exists in the form of primary and secondary Al3Er phase, which play significant roles of refining and strengthening the fusion zone. A characteristic Equiaxed Zone (EQZ) is obtained beside the fusion boundary between the partially melted zone and the fusion zone (FZ) due to the addition of Er.

A series of fiber laser–metal inert gas (MIG) hybrid welding experiments were carried out on the commercially pure titanium (CP-Ti) sheets to investigate the effects of the welding parameters, such as MIG welding current, welding speed, laser-arc distance, defocused distance of laser beam and gap, on the bead appearance, weld shape, and tensile properties of the welded joints. The results show that fiber laser–MIG hybrid process parameters were of considerable importance for the bead appearance, weld width, and elongation of the welded joints. However, ultimate tensile strength (UTS) of the welded joints in CP-Ti was not obviously influenced by the process parameters owing to a higher microhardness in the fusion zone compared to the base metal.