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Welding of AlSi10Mg alloys fabricated by additive manufacturing (AM) has been recently conducted to meet the demands for joining or repairing them. However, high susceptibility to porosity occurring in weld metal (WM) poses a significant challenge for fusion welding of AM AlSi10Mg alloys. The laser metal deposition (LMD) process has emerged as a promising welding solution due to its low dilution rate for reducing the porosity. In this study, LMD welding of AM AlSi10Mg alloys was carried out employing different heat inputs with five and eight tracks. The study systematically assessed the impact of heat input on porosity, microstructure, and mechanical properties of the welded joints. The results show that the decrease of heat input from 180 to 75 J/mm results in a substantial reduction in porosity from 7.0 to 2.1%. This reduction leads to a 29.4% increase in ultimate tensile strength (UTS) and an 11.7% increase in elongation index (EI). Furthermore, the upper region of joints with eight tracks possessing low heat input displays lower porosity and superior mechanical properties than the bottom region with relatively high heat input. The WM with eight tracks exhibits refined α-Al cells and Si-rich eutectic phases, improved connectivity of Si-rich networks, and increased solid solution strengthening, compared to the five-track joints with higher heat input. As a result, low heat input of the upper region in the LMD welded joints has been effective in minimizing hydrogen pores, enhancing WM microstructure, and improving the mechanical properties of welded joints in AM AlSi10Mg alloys.

• Microcracks in LPBF-processed HEA were significantly eliminated via HIP treatment. • LPBF-processed HEA after HIP exhibits high UTS of 1149 MPa and FE of 22.9%. • The property improvement is attributed to the crack closure and precipitation strengthening. Hot isostatic pressing (HIP) is usually applied to reduce the defects including cracks and pores in the materials prepared by laser powder bed fusion (LPBF). In the present research, in order to improve the relative density and mechanical property, HIP was employed on the LPBF-processed Al-Cr-Fe-Ni-V high-entropy alloy (HEA) with microcracks and pores. The microstructure evolution and property improvement induced by HIP were investigated. In the LPBF-processed HEA, the microcracks were caused by residual stress and element segregation, and these microcracks as well as the pores reduced significantly after HIP treatments. Remarkably, HIP temperature has a more critical effect on the microcrack closure than the holding time, thus, microcracks and pores still existed after HIP-1 treatment (1273 K, 8 h), while HIP-2 treatment (1473 K, 4 h) could close the microcracks significantly. The crack closure was attributed to the interfacial diffusion of the alloying element under high temperature accompanied by high pressure, and the degree of element diffusion at both interfaces of the cracks determined the bonding strength after crack closure. Higher temperatures at high pressure induced more adequate element diffusion and higher bonding strength. The above high temperature and high pressure also induced the growth of the L1 2 phase and the precipitation of the B2 phase in HEA. Consequently, the tensile strength and elongation of the LPBF-processed HEA after HIP-2 treatment were simultaneously enhanced (80.7% and 222.5% higher than that of LPBF-processed HEA, respectively). This could be attributed to the combined effect of microcrack/pore closure and precipitation strengthening. The strengthening effect of the B2 phase and L1 2 phase accounted for 53% (dislocation by-pass mechanism) and 47% (dislocation shearing mechanism) of the total precipitation strengthening, respectively. [ABSTRACT FROM AUTHOR]

In this study, we propose Fe–Mn-Cr/Ni as an economical drill collar overlay material applied via metal-cored arc welding (MCAW). A series of Fe–Mn-Cr/Ni overlay alloys with different Ni contents were prepared by MCAW, and their microstructure, non-magnetic, and wear properties were systematically investigated. The results show that the addition of Ni element can effectively improve the austenitization of the Fe–Mn-Cr/Ni overlay alloy and inhibit the formation of ferromagnetic hexagonal martensite (ε) and body-centered ferrite (α), thus improving the non-magnetic properties of the Fe–Mn-Cr/Ni overlay. With the increase of Ni addition from 0.6 to 4.7 wt.%, the average grain size gradually increases from 21.69 to 49.97 µm, and the overlay microstructure gradually evolves from columnar-like ε-martensite to wide ε-martensite band and eventually almost austenite. This change in microstructure as Ni content increases contributes to the reduction of relative permeability from 2.225 to 1.057 due to the increased austenite contents, at the cost of increased wear rate from 2.61 × 10−5to 4.55 × 10−5mm3·N−1·m−1due to the decay of wear-resistant ε-martensite skeleton. By controlling the Ni content, this work demonstrates the potential of preparing Fe-based austenitic wear-resistant layers with high Mn content and broadens the scope of austenitic non-magnetic deposited alloys for surface overlay strengthening or repairing of Fe-based non-magnetic drilling tools.

The absorption of laser energy by pure copper powders has a huge impact on the formation of high quality pure copper parts by selective laser melting. In this paper, surface modification technology was used to treat pure copper powder to improve the laser absorption effect of pure copper powder. It was found that modifying the surface of pure copper powder to generate a layer of CuO film effectively improved the absorption of laser energy by pure copper powder. Uniform and dense CuO films improved the quality of selective laser melting pure copper parts, which solved the problem of preparing pure copper powders for selective laser melting of high-density parts. The microstructure of selective laser melting high-density pure copper parts consisted of fine columnar and cellular crystals. The presence of subcrystals and dislocations was found in localized areas. The results of the physical phase analysis showed that the CuO phase existed in the parts prepared from the surface-modified pure copper powder, and the presence of the nano-CuO phase also enhanced, which effectively improved the microstructure and properties of the constituent selective laser melting pure copper parts.

A new type of Al–Mg-Er-Zr alloy was welded by a gas metal arc welding (GMAW) process. The effect of GMAW welding on the microstructure, microtexture, and mechanical properties was investigated and compared with the base material (BM). The results show that GMAW welding leads to a change in the grain shape, grain orientations, phase composition, microtexture, microhardness, and tensile properties. The weld metal (WM) exhibits coarse grains, high proportion of high angle grain boundaries (HAGBs), and low intensities of random textures compared with the BM. In addition, the recrystallization occurs in the HAZ due to the welding heat effect; grains and secondary phases are coarsened compared with the BM. The texture evolution in the HAZ exhibits the disappearance of the deformation textures, along with the transformation and competitive growth of P, R, and Cube recrystallization textures. The average ultimate tensile strength (UTS) of the GMAW joints is 280.7 MPa, and the lowest hardness of 75.2 HV is located in the WM. Compared to the BM, the welded joints in the Al–Mg-Er-Zr alloy produce reduced microhardness and tensile properties. However, the strength coefficient of the welded joints reaches 0.75, together with the elongation index (EI) of 11.4%, implying GMAW welding for the Al–Mg-Er-Zr alloys achieves a good combination of strength and ductility.

Laser metal deposition process was introduced to join AlSi10Mg alloys fabricated by powder bed fusion-laser beam/metal to improve the tensile strength of laser welded joints. The size and the porosity of the hydrogen pores in the weld seam are significantly reduced by laser metal deposition welding. The ultimate tensile strength of the welded joint by using laser metal deposition reaches 318.8 MPa, and the microhardness of the weld seam ranges from 99.5 to 105.4 HV. Compared with single-pass welding, the ultimate tensile strength and hardness are increased by 60.6% and 27.6%. This is mainly attributed to the reduced porosity, refined α-Al structures and increased connectivity of the Si-rich networks of the weld seam achieved by laser metal deposition welding.

Laser metal deposition process was introduced to join AlSi10Mg alloys fabricated by powder bed fusion-laser beam/metal to improve the tensile strength of laser welded joints. The size and the porosity of the hydrogen pores in the weld seam are significantly reduced by laser metal deposition welding. The ultimate tensile strength of the welded joint by using laser metal deposition reaches 318.8 MPa, and the microhardness of the weld seam ranges from 99.5 to 105.4 HV. Compared with single-pass welding, the ultimate tensile strength and hardness are increased by 60.6% and 27.6%. This is mainly attributed to the reduced porosity, refined α-Al structures and increased connectivity of the Si-rich networks of the weld seam achieved by laser metal deposition welding.

Surface pretreatment is of great significance for improving the welding quality of metal materials, especially aluminum alloys. At present, the welding process is introduced to join the laser powder bed fusion (LPBF) AlSi10Mg alloys or their repair during manufacturing or service. However, the high susceptibility of hydrogen pores is one of the most important problems encountered in the fusion welding process of LPBF AlSi10Mg alloys. To clarify the influence of the surface state of the base metal on the hydrogen pore characteristics, the LPBF AlSi10Mg sheets were pretreated by chemical cleaning treatment (CCT), mechanical polishing treatment (MPT), and chemical cleaning treatment after mechanical polishing treatment (MPT-CCT) before laser welding. Subsequently, the hydrogen pore characteristics, microstructure, and micro-hardness of the welded joints were investigated. The experimental results show that laser welding with MPT-CCT significantly reduces the porosity and pore diameter. In addition, MPT-CCT can eliminate most of the broken and discontinuous surface oxide film and Mg enrichment. In summary, the necessity of MPT-CCT for LPBF AlSi10Mg alloys is analyzed systematically, which is of great significance to improve the welding quality.

Zinc (Zn) is a potential bioresorbable metal material (BMM) with a degradation rate lower than magnesium and higher than iron. However, clinical applications of pure Zn are limited due to its poor mechanical properties and localized degrading tendency. Overcoming these drawbacks is made possible by the process of alloying. The Zn-0.6Li-0.5Mg alloy samples were prepared using the laser powder bed fusion (LPBF) process in this work. The innovative technique combining fast solidification produced by LPBF and alloying with Li and Mg was presented to enhance the mechanical properties of Zn in this work. The relative density, microstructure, mechanical properties, and corrosion resistance of LPBF-built Zn-0.6Li-0.5Mg alloy were investigated. According to the results, the LPBF fabricated Zn-0.6Li-0.5Mg alloy with fine equiaxed α-Zn grains were uniformly distributed with precipitated Mg2Zn11and LiZn4at grain boundaries. More interestingly, the average grain size of α-Zn was recorded at 7.2 ± 3.2 μm with Li and Mg. Due to the rapid solidification process, Mg dissolved primarily in the Zn matrix and developed a supersaturated solid solution. As a result, with the addition of Li and Mg, the mechanical properties of the Zn matrix increased considerably. When combined, Zn-0.6Li-0.5Mg alloy can be an attractive candidate for bioresorbable medical implants in orthopedic applications.

The microstructure and the mechanical properties of α-phase Cu–5Sn alloy, Cu–10Sn alloy, and Cu–15Sn alloy (wt.%) prepared by selective laser melting have been studied in this work. Under the same process condition, the laser absorption of the alloys increases continuously with the increase in Sn content. The optimal process parameters of the three alloys were obtained by Response Surface Method. The Sn content was found to have a significant effect on the relative density of the Cu–Sn alloys, as well as the laser power. The effect of laser power on the relative density of the alloys is weakened by the increase in laser absorption as the Sn content increases. Comparing the melt pool of the three alloys, they all show mainly columnar grains. As the Sn content increases, the size of the columnar grains becomes larger, and when the Sn content reaches 15 wt%, the columnar grains can penetrate through several melt pools. With the increase of Sn content from 5 wt% to 15 wt%, the tensile strength of the alloy increased from 382 MPa to 738 MPa, but the plasticity decreased significantly and the elongation decreased from 26% to 9%. As the Sn content increases from 5 to 15 wt%, the amount of solid-soluble Sn in the α-phase alloy increases, creating a lattice distortion stress field that effectively prevents dislocation movement. Thus, the stress field effectively increasing the yield and tensile strength of the alloy. Meanwhile, the increase in Sn content leads to the appearance of many brittle, hard and rich phases on the micron scale and precipitation from grain boundaries within the lattice, resulting in an increase in strength and a decrease in plasticity of the alloy. In conclusion, Cu–10Sn alloy has more excellent tensile properties and higher yield and tensile strengths with good ductility compared to Cu–5Sn and Cu–15Sn alloys.

Graphical Abstract:

Cold metal transfer (CMT) welding of AlSi7Mg alloy sheets prepared by selective laser melting (SLM) was employed using ER4047 and ER5356 filler wire. Effect of the filler wires on hydrogen pores, microstructures and mechanical properties of welded joints was studied. As a result, CMT welding of AlSi7Mg alloy sheets using ER5356 wire reduces the porosity, refines the grains, increases the fraction of high angle grain boundaries (HAGBs), modifies the eutectic Si-rich morphology, and improves the solid solution strengthening of Si elements in the α-Al matrix of the microstructures in the weld metal (WM). Additionally, the morphology of eutectic Si-rich phases in heat affected zone (HAZ) of the welded joint is noticeably changed from the continuous cellular networks in base metal (BM) to totally globularized particles, as a result of the increased welding heat effect with decreasing distance to the WM. Compared with the ER4047 wire, the welded joint with ER5356 wire achieves higher WM hardness and higher ultimate tensile strength (UTS), which have been increased by 13.9 % and 18.6 %, respectively. The enhanced mechanical properties of the welded joints with ER5356 wire are mainly attributed to the reduced porosity and the improved microstructures in the WM.

In order to explore the application of tungsten (W) fabricated by laser powder bed fusion (LPBF), W with different geometrical shapes and different support structures were prepared, and the corresponding microstructural characteristics were investigated. Coarse columnar grains and fine grains exist simultaneously in the cylinder or bulk W specimens fabricated by bi-directional scanning. The single-directional scanning used in wall-shape specimen fabrication facilitates the epitaxial growth of W grains, forming regular elongated columnar grains. Cracks were found in all the specimens, the formation of cracks in W during LPBF is determined by a combination of the localized stress distribution and the intrinsic strength/ductility of the W phase. Cracks are concentrated at the grain boundaries where the coarse columnar grain and fine grains are adjacent. With the specimen size increased from cylinder (slender cylinder, squat cylinder), wall (thin wall) to the bulk specimen (with 0–2 mm support), more cracks were found due to higher residual stress. Cracks could relieve the residual stress dramatically, which leads to the decrease of the dislocation density, therefore, with the increase in specimen size, both low angle grain boundaries (LAGBs) and the geometrically necessary dislocation (GND) density decrease. Adding support structure in bulk W could decrease the cooling rate and increase the cooling time. Low cooling rate can reduce the stress level as well as the generation of cracks. Long cooling time could provide sufficient time for dislocation nucleation and movement to form LAGBs structure. Therefore, there are fewer cracks and higher GNDs density/LAGBs portion inside the W phase with a higher support structure.

To improve the efficiency and accuracy of the numerical simulation for the laser powder bed fusion (LPBF) process, an optimized segmented heat source (OSHS) model is proposed in this work. The results show that the geometrical size and temperature distribution contour of the calculated cross-sectional molten pool are almost the same as those calculated by the moving heat source (MHS). Under the same mesh scheme, the calculation efficiency of the OSHS model improves about 9 times to that of the traditional MHS model. Moreover, the OSHS model can achieve stable calculations with the medium-size elements grid, which can reduce the required calculation time to one-third of the fine mesh scheme and achieve almost the same thermal-mechanical calculation result. This model was successfully applied on the simulation of the LPBF single layer multi-tracks thermal-mechanical numerical simulation. To verify the calculated results, the sample of the same size was prepared using 316L stainless steel by LPBF technology. The surface residual stress components of the as-built sample were measured by X-Ray Diffraction (XRD). The calculated residual stress curves were in good agreement with the measured results. The simulation and experimental results indicated that the primary surface residual stress component was the tensile stress along the laser scanning direction, which was about 280 MPa. The shear stress was concentrated at the corners of the as-built sample. Therefore, the OSHS model proposed in this work greatly improved the calculation efficiency and obtained very accurate results for the thermal-mechanical simulation of the LPBF process.

Metal inert gas (MIG) welding of a novel Al-5.82Mg-0.61Zn-0.14Er-0.11Zr alloy was performed using ER5E61 and ER5B71 filler wires. The effect of the two filler wires on microstructures and mechanical properties of MIG welded joints was investigated. The study shows that fully penetrated joints are obtained by MIG welding process filled with ER5E61 and ER5B71 wires. Compared with ER5B71, the weld metal (WM) with ER5E61 exhibits a coarse structure, high solid solution of Mg and Mn elements. After the tensile test, the WM with ER5E61 and ER5B71 wires is composed of elongated coarse grains with a higher proportion of LAGBs. In addition, the lattice rotation occurring within the grains, indicating that single grain has an unevenly plastic deformation after the tensile test. The average microhardness of the WM is 83.4 HV and 82.9 HV for ER5E61 and ER5B71wire, which is the lowest microhardness in the MIG welded joint. The average ultimate tensile strength (UTS) and elongation index (EI) of the MIG joints are 327.7 MPa and 8.5% for ER5E61 wire, and 314.3 MPa and 8.2% for ER5B71 wire, suggesting the MIG welded joint with ER5E61 wire achieves a good combination of strength and ductility. Quantitative assessments of the effects of different strengthening mechanisms on the strength reveal that dislocation strengthening and solid solute strengthening are the main factors to obtain a higher strength of welded joints with ER5E61.

Dissimilar joining of 6 mm thick steel/Al butt joints was carried out using a novel laser offset welding process. The effect of the different locations at the interface on the intermetallic compound (IMC) layers of the joints produced by two different laser powers was investigated. Microstructure inhomogeneity of the IMC layers was investigated in terms of phase morphology, thickness, grain size, main component and phase compositions. As a result, the IMC layer at the interface has the same phase types consisting of η-Fe2Al5and θ-Fe4Al13phase for the three locations produced by two laser powers. However, the morphology of the θ-Fe4Al13phases, the grain size and the thickness of the η-Fe2Al5layers, and the predominant component in the IMC layers is strongly affected by the laser powers and the locations at the interface. The highest UTS of 85.5 MPa is obtained at the middle location due to the formation of the thinner η-Fe2Al5layers and the minimum amount of θ-Fe4Al13phases. Decreasing laser energy inputs effectively improves the IMC layer uniformity, and the influence of locations at the interface on the IMC layer thickness will be weakened with further decreasing the energy inputs. The heating temperature at the interface has a very important impact on the thickness of the η-Fe2Al5layer attributed to the ferrite or austenite phases appeared in the steel substrate affecting the growth rate of the η-Fe2Al5layers.

In order to join the similar magnesium alloy, a novel Zn-Mg-Al filler metal was designed and applied to braze AZ31B plates by using high-frequency induction brazing technique. The microstructure, phase constitution and fracture morphology of the brazed joint were investigated. The experimental results show that MgZn2 phase in the original filler metal is completely consumed in the brazing process. Moreover, α-Mg solid solution and α-Mg+MgZn eutectoid structure formed in the brazing region due to the intensive alloying between the molten filler metal and the base metal in the brazing process. Test results indicate that the shear strength of the brazed joint is 56 MPa. The fracture morphology of the brazed joint shows intergranular fracture mode, where crack originates from the hard α-Mg+MgZn eutectoid structure. [Copyright &y& Elsevier]

Abstract: In this study, nickel-base cored wires were prepared by using NiCr strip to wrap metal powders of nickel (Ni), chromium (Cr), molybdenum (Mo), and chromium boron (CrB). Nickel-base coatings were prepared by electric arc spraying. Microstructures of Ni-Cr-Mo and Ni-Cr-B coatings were investigated using scanning electron microscopy (SEM), energy-dispersive analysis (EDAX), and x-ray diffraction (XRD) analysis. The coatings have a compact surface and presented a bonding strength higher than 40 MPa. Potentiodynamic polarization measurements and salt-spray test were carried out to determine the corrosion behavior of the coatings. The results showed that Ni-base coatings containing Mo (5%) or B (2-4%) had better antichlorine ion corrosion performance than that of Ni-base coatings without Mo element, and PS45 (Ni-Cr-Ti) coating. The antichlorine ion corrosion coatings could be used for resolving the corrosion protection problem of the equipment and piping contacting sour, alkali, salt liquid in petrochemical engineering applications.

Al12Si was deposited by cold spray process. The influence of spray parameters on coating build up and coating microstructure was investigated. The process gas temperature was the crucial parameter for deposition of Al12Si. Increasing process gas temperature led on the one hand to a strong increase in the coating thickness, on the other hand to increasing coating porosity. In addition, the spray distance and the process gas flow rate could also have a significant influence, especially when spraying with higher process gas temperatures.