The proposed paper illustrates the fabrication and heat treatment of high strength Al-Cu-Mg alloy produced by selective laser melting (SLM) process. Al-Cu-Mg alloy is one of the heat treatable aluminum alloys regarded as difficult to fusion weld. SLM is an additive manufacturing technique through which components are built by selectively melting powder layers with a focused laser beam. The process is characterized by short laser-powder interaction times and localized high heat input, which leads to steep thermal gradients, rapid solidification and fast cooling. In this research, 3D Al-Cu-Mg parts with relative high density of 99.8% are produced by SLM from gas atomized powders. Room temperature tensile tests reveal a remarkable mechanical behavior: the samples show yield and tensile strengths of about 276 MPa and 402 MPa, respectively, along with fracture strain of 6%. The effect of solution treatment on microstructure and related tensile properties is examined and the results demonstrate that the mechanical behavior of the SLMed Al-Cu-Mg samples can be greatly enhanced through proper heat treatment. After T4 solution treatment at 540°C, under the effect of precipitation strengthening, the tensile strength and the yield strength increase to 532 MPa and 338 MPa, respectively, and the elongation increases to 13%.
Laser produced plasma (LPP) light sources for extreme ultraviolet (EUV) lithography currently has been extensively studied. Most of the studies are based on CO2 laser induced plasma from mass limited tin targets. In this work, a droplet dispenser that produces uniform droplets size of about 150μm was established. A pulsed TEA-CO2 laser and a Nd: YAG laser irradiated the droplets producing plasma respectively to get EUV emission. An X-ray Spectrometer and EUV photodiodes were used to collect the spectra and EUV radiation. The different EUV spectral composition and angular distribution of EUV emission from plasmas induced by the CO2 and Nd: YAG laser were studied.
A series of technological parameters in controlling plasma in deep penetration CO2 laser welding at an arrange of power level from 1 kW to 5 kW were investigated by using a precise declined-blow system by which the gas-assisting pressure and nozzle position can be precisely adjusted for various gas species and laser power levels. The mechanism of plasma-control by assist gas was also clarified on the basis of pressure measurement of assist gas, estimation of metallic vapor pressure in the cavity, and monitoring of plasma brightness by using phototransistors. It was found that the effect of assist gas on penetration depth can be divided three regions with the change of the assist gas pressure. No matter what gas species were used, only is the gas pressure slightly higher than the vapor pressure, plasma can be suppressed by forcing the vapor to flow away from the incidental laser beam along the cavity rear wall, then optimum weld beads can be obtained.