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In this study, a ZK60 Mg alloy fabricated by laser powder bed fusion (LPBF) is subjected to in-situ aging treatment by preheating the substrate. The effects of preheating temperature on the microstructure, mechanical properties, and corrosion resistance of the LPBF-processed ZK60 alloy are systematically analyzed. The results show that at the preheating temperatures of 35, 90, and 180 °C, the average grain size of the samples does not change much, ranging between 7.0 and 8.2 μm. As the preheating temperature increases, the mechanical properties of the alloy increase. The specimens treated at a preheating temperature of 180 °C exhibit a yield strength (YS) of 201 ± 5 MPa, ultimate tensile strength (UTS) of 291 ± 7 MPa, and elongation (EL) of 14.7 ± 0.8%. This is attributed to the precipitation of a large amount of β' 1 phase in the alloy during the aging state in the LPBF process. However, the corrosion resistance first improves and then deteriorates with the increase in the preheating temperature. Under a preheating temperature of 90 °C, the corrosion resistance is improved due to the reduction in the galvanic corrosion area by the precipitated phases. When the preheating temperature is increased to 180 °C, the precipitated phases and α-Mg form a large number of microgalvanic cells, which increases the active center for corrosion and deteriorates the corrosion resistance. These findings indicate that the desired mechanical properties and corrosion resistance of the LPBF-processed ZK60 alloy can be obtained by selecting an appropriate preheating temperature. • The cracks significantly reduce in LPBF-processed ZK60 alloy by substrate preheating. • The mechanical properties increase with increasing preheating temperature. • The corrosion resistance first improves and then deteriorates. • β' 1 phase is beneficial to mechanical properties but deteriorates corrosion resistance. [ABSTRACT FROM AUTHOR]

In order to solve the problems of die and tooling manufacturing and assembling for the foil forming, especially for the foil micro forming, high-pressure water jet forming (HPWJF), a new die-less forming process for foil parts is proposed. In the forming process, liquid medium such as water and oil is utilized as a flexible tool to deform the ultrathin foil. In this paper, the computational fluid dynamics (CFD) software Fluent was used to simulate the water jet generation in the water jet nozzle and high-speed water impacting on a rigid surface. And then, the effects of jetting distance on the jetting pressure were obtained. To measure the precise mechanical parameters of copper foils, a digital speckle test method was used to detect the tensile process. Local bulging experiment was conducted for the copper foil with a thickness of 50 μm. When the inlet pressure is 8.5 MPa, the suitable jetting distance is 40 mm for the 50-μm-thick copper foil. In such conditions, the bulging height of the copper foil is 1.20 mm in the experiment. The fluid-solid coupled method by using Fluent and Abaqus was applied to simulate the deformation of the copper foil. The errors between the simulated results and the experimental values are lower than 10 %. Furthermore, both the experiment and simulation for micro stretching of 30-μm-thick copper foil were performed. The cylinder die with a diameter of 3 mm and a height of 1.5 mm is used to form the copper foil. Results show that the copper foil cracks when the jetting distance is 24 mm, and the inlet pressure is 12 MPa. With the increase of the inlet pressure, the drawing depth of the copper foil gradually increases, and the bottom of the cylinder part thins gradually, and the wrinkling of the flange of the cylinder part becomes more and more severe. [ABSTRACT FROM AUTHOR]

• Four powder feeding modes were designed and selected by contrast arc stability. • A multi-stream powder feeding method was designed and verified. • The gap of ferrite content between the arc and laser zone was narrowed to 1.3 %. • The strength of nitrided joint was 24.5 % higher compared with non-nitride joint. The effect of powder feeding mode on the stability and nitrogen distribution of the high nitrogen steel (HNS) welding process was evaluated. The N loss of the joint was serious while the tensile strength was reduced to about 63.4 % in the absence of any effective measure. Four different configurations of powder feeding were designed to study the feasibility of powder feeding in the laser CMT hybrid welding process. And the powder feeding process was analyzed by arc shape and current-voltage curves which were collected by the Acuteye V4.0 welding observation system at 4000 frames/s. The most stable configuration was to fill the powder behind the arc. But non-uniformity was observed in the microstructure and properties in these configurations. The difference of ferrite content and tensile strength between the arc zone and laser zone reached 4.9 % and 150 MPa, respectively. A multi-stream powder feeding assisted laser-CMT welding method was proposed to improve the powder distribution and arc stability. The powder distribution was similar to the theoretical range and narrowed the ferrite content gap between the arc and laser zone to 1.3 %, and also the arc became stable even when a proportion of N 2 was used. The tensile strength of the HNS welded nitride by CrN powder could reach 1198 MPa, which was 24.5 % higher than that of the non-nitride joint. However, the combination of N 2 and powder nitriding needs to be explored in the future work. [ABSTRACT FROM AUTHOR]

Wire-based additive manufacturing (AM) presents promising opportunities for making large components with high-price materials, such us aluminum alloys containing expensive rare earth element of scandium (Al-Sc alloy). However, wire-based AM of structurally sound and defect-free aluminum components is still challenging. In this work, an oscillating laser-arc hybrid additive manufacturing (O-LHAM) process was developed to fabricate thin-wall parts of Al-6Mg-0.3Sc alloy. To show the effect of oscillating laser beam on macro/micro-structure, porosity and mechanical properties, wire and arc additive manufacturing (WAAM) of Al-6Mg-0.3Sc alloy part was also performed for comparison. The results showed that the surface roughness of O-LHAM samples was reduced by 34.7% and the effective wall width was increased by 20% when maximum width of the wall was same with WAAM. The porosity was significantly mitigated and the microstructures was refined and homogenized due to the string effect of beam oscillating in the molten pool. The as-deposited wall of Al-Sc alloy showed an ultimate tensile strength of more than 350 MPa, reaching an exceptional level among the as-deposited aluminum alloy. The O-LHAM samples showed a higher elongation and lower anisotropy, which are resulted from the mitigated porosity and homogenized microstructure. [Display omitted] ● Al-6Mg-0.3Sc alloy thin-wall part was fabricated by O-LHAM. ● The surface quality of O-LHAM sample was improved in comparison with that of WAAM. ● The porosity was mitigated due to the stirring effect of oscillating laser beam. ● The microstructure was refined and homogenized in O-LHAM sample. ● The as-deposited Al-6Mg-0.3Sc alloy showed an UTS of more than 350 MPa. [ABSTRACT FROM AUTHOR]

The laser powder bed fusion (LPBF) was employed to process the ZK60 Mg alloy. The effect of heat treatment on the microstructure and hardness of LPBF ZK60 Mg alloy was investigated. The results showed that the grain boundary of LPBF ZK60 Mg alloy was composed of a network Mg 7 Zn 3 phase. Three types of precipitated phases were distributed inside the grains: the type-Ⅰ is Zn-rich precipitated phase with Zr-rich core, the type-Ⅱ is Zn-rich precipitated phase without Zr, the type-Ⅲ is Zr-rich particle. When the solution treatment was used, the Mg 7 Zn 3 phase at the grain boundary melted and merged into the matrix. The precipitated phase in the grain mainly evolved into Zn-rich phase with Zn 2 Zr core. Continue with the aging heat treatment, the rod-shaped β 1 ′-MgZn precipitated phase separated out from the α-Mg matrix. The length of the rod-shaped precipitated phase undergone double aging is longer and the quantity is more than that of the single aging. The rod-shaped β 1 ′-MgZn precipitated phase significantly improved the mechanical properties of LPBF ZK60 Mg alloy. The average hardness increased from 0.88 ± 0.025 GPa to 1.01 ± 0.010 GPa and the ultimate tensile strength increased to 287 ± 4 MPa after the solution treatment plus double aging heat treatment. • Microstructure evolution of LPBF fabricated ZK60 under different heat treatment is explored. • There are three types of precipitated phases in LPBF fabricated ZK60. • More precipitated phases can be obtained under T4 plus double aging. • LPBF fabricated ZK60 will achieve the best microstructure after T4 plus double aging. [ABSTRACT FROM AUTHOR]