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The microstructure and corrosion behavior of Y-modified ZK60 Mg alloy prepared by laser powder bed fusion (LPBF) are studied. By controlling the content of Y, the quantity, distribution, and type of precipitates are regulated, and the corrosion resistance is improved. Specifically, the ZK60 alloy with 1 wt% Y exhibits excellent corrosion resistance, which is mainly due to the formation of a continuous network of rare earth-containing precipitates at the grain boundaries that form corrosion barriers to impede corrosion and induce grain refinement. In addition, the passivation and stability of the surface film are improved after the addition of Y. • The microstructure and corrosion behavior of LPBF-processed ZK60- x Y are studied. • The LPBF-processed ZK60-1Y alloy exhibits excellent corrosion resistance. • Continuous rare-earth precipitates at grain boundaries form corrosion barriers. • The microcracks are suppressed after adding an appropriate amount of Y. [ABSTRACT FROM AUTHOR]

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]

• High nitrogen steel weld was nitrided by MnN powder accompanied with N pores. • The N content increased by 17%, but the distribution of N was uneven. • N pores were absorbed inhibited by Ti and form the precipitation phase (TiN). The welding of high nitrogen steel (HNS) was accompanied with N loss and porosity, leading to the mechanical properties degradation. In this study, laser-arc hybrid welding of HNS with MnN powder was evaluated. The experimental results indicated that the addition of MnN powder could increase the N content by 17% compared with the non-nitride joints. And no MnN particles were detected in the joint. There were mainly two kinds of pores in the weld of HNS. The irregular pore was suppressed by adjusted welding speed and laser power. The degree of austenitization and the N pores in joint increased with the increase in the N content, because the MnN powder could promote the formation of N pores. The reactive pore was originated from the thermal decomposition of the MnN powder with a temperature more than 800℃. And the micro-pore was precipitated along the interface between austenite and ferrite because of the supersaturated N in ferrite. Adding Ti could give priority to the formation of the TiN phase and inhibit the formation of N pores. The tensile strength of the joint was increased to 1072 MPa. The impact property of the nitrided joint was also slightly improved. However, the tensile strength of the arc zone was better than that of the laser zone due to the uneven distribution of N. [ABSTRACT FROM AUTHOR]

Abstract Nanosecond laser-induced fabrication of superhydrophobic surfaces has become a research focus of functional surfaces studies in recent years. In this study, we present a novel and highly efficient method for fabricating a superhydrophobic functional aluminum alloy surface. The method is based on large spot diameter (d = 960 μm) infrared nanosecond laser high-speed (linear velocity v = 3 m/s) scanning and ablation of the surface followed by low surface energy agent chemical treatment to attain a superhydrophobic state on the aluminum alloy surface. The textured roughness surfaces show three specific micro-morphology characteristics including corrugated, mastoid and flat zones all densely covered by cauliflower-like nanostructures. The hierarchical micro- and nanostructured surfaces demonstrated outstandingly stable superhydrophobicity during long-term exposure to an ambient atmosphere. The proposed method proves that large spot diameter high-speed scanning low-cost nanosecond lasers are also suitable for fabrication of large area metallic superhydrophobic surfaces for practical industrial application. Highlights • Superhydrophobic surface can be obtained by large spot nanosecond laser treatment. • The microstructure of the surface was comprised of corrugated, mastoid and flat zones. • Three zones were all covered by cauliflower-like nanostructures. • Superhydrophobic aluminum surface is of good stability. [ABSTRACT FROM AUTHOR]

Herein, we propose a method for producing W C composite ceramic coatings on tungsten alloy surfaces using directed energy deposition (DED). Different microstructures of DED single tracks were obtained with different line energy densities. Two parts of DED tracks were discovered, which contained the W C fusion zone and the WC-Ni-Co melting injection zone. The W C fusion zone mainly comprised four typical phases, WC, W 2 C, W, and C(diamond, graphite (D, G)), which were present in the microstructures of the tracks in different combinations. The key factor for determining the microstructure evolution was C content. With higher line energy density, more tungsten alloy melted, which decreased C content in the melt pool. As C content decreased, the composition of the microstructure transformed to C(D, G) + WC + W 2 C → WC + W 2 C → W 2 C + W + a small amount of γ-(Ni, Co). C content gradually decreased from the top to the bottom of the melt pool, resulting in a gradient microstructure transition. The microstructure and property could be tuned by controlling the C content. The hardness was the highest, 2300 HV, at 40.7 at.% C with WC-W 2 C eutectoid. This study provides practical insights for producing coatings on tungsten alloy surfaces with optimized process parameters and for tailoring mechanical properties. • DED W-C composite ceramic material on the surface of W alloy was prepared. • W-C fusion zone and WC-Ni-Co melting injection zone of DED tracks were discovered. • The key factor for determining the microstructure evolution was C content. • The hardness of the microstructure was the highest, 2300 HV, with 40.7 at.% C. [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]

The magnesium alloy of ZK60 components manufactured by selective laser melting (SLM) have been investigated in this work. The microstructure and the mechanical properties of the SLM-processed samples are determined. The ZK60 samples prepared had fish-scale features along the build direction along with homogeneous and refined grains. The microstructure consisted of equiaxed α-Mg matrix with a size of 3–8 μm and nanoscale precipitates. The nano-precipitates had a core-shell structure with a Zn 2 Zr core embedded in a MgZn 2 shell. The optimal micro-hardness and the compressive yield strength of the SLM ZK60 sample at room temperature are 90 Hv and 172.59 MPa, respectively, which is superior to cast ZK60 because of grain refinement strengthening and precipitation strengthening. [ABSTRACT FROM AUTHOR]

• Dissimilar-metal welding of Ni-Cr-Mo and Cu-Cr-Zr alloy was studied. • Comparative studies of laser welding without and with oscillation were carried out. • Laser welding with oscillation made even microstructure without macro-segregation. • Hardness distribution and tensile property of dissimilar-metal welding were tested. Laser processing of welding with oscillation was adopted to weld dissimilar metals of Ni-Cr-Mo and Cu-Cr-Zr so as to prevent the generation of the macroscopic segregation. Analyses of morphology, element distribution and mechanical property were carried out to investigate the effect of oscillation on dissimilar-metal welding. The results indicated that with the application of oscillation of laser, the poor mixing zone and the partial melting strengthening phases were obviously reduced, and the distribution of main constituent elements was more uniform. Due to the better effect of solid solution strengthening, the maximum increment of the tensile strength and elongation could approximately be up to 20% and 45%, respectively. [ABSTRACT FROM AUTHOR]