A 7075/5356 aluminum alloy laminated composite was fabricated by alternately depositing a 7075 wire and a 5356 wire layer by layer using wire arc additive manufacturing (WAAM). The microstructure and mechanical properties of the produced components under as -deposited and heat -treated conditions were investigated. The results revealed that the grain morphology of the specimen was mainly composed of equiaxed grains in each layer, while the grain size of the interlayer region was reduced due to the heterogeneous nucleation relying on the partially remelted previous layer. Moreover, a reduced amount of second phase was observed due to decreased Zn and Cu alloying elements content in this region, which resulted in a gradient change in microhardness distribution. The tensile strength and elongation of the heat -treated samples in vertical and horizontal directions were 321 MPa, 10.12 %, and 377 MPa, 9.72 %, respectively. The results indicated good comprehensive mechanical properties, which is promising for further application of WAAM fabricated laminated metal composite.

The increasing demand for high-efficiency and high-quality wire-based arc directed energy deposition processes presents a significant challenge to the plasma arc, which is greatly influenced by plasma gas composition. This paper introduced mixed gases of helium (He) and argon (Ar) into the plasma gas for the deposition of Ti-6Al-4 V. The effect of plasma gas composition on the deposition characteristics concerning arc electrical characteristics, keyhole formation, metal transfer, bead geometry, and surface waviness were investigated. Results demonstrate that the arc voltage and heat input exhibited a linearly increasing tendency with the increase of He in the plasma gas, attributed to a higher ionization potential and thermal conductivity. The threshold current value for keyhole formation was effectively increased by adding He to the plasma gas. The keyhole formation was completely suppressed as the He content was higher than 50

7075 aluminum alloys with varying TiC particle additions were fabricated by simultaneously depositing a standard 7075 wire and a TiC treated wire at different wire feed speed ratios. The effects of TiC content on the microstructure and mechanical properties of 7075 alloy were investigated. Results indicated that the addition of TiC particles can effectively refine the grain structure through heterogeneous nucleation, and the grain refinement effect was enhanced with increasing TiC particle content in the range of 0-0.70 wt%. Moreover, TiC particles can restrain the continuous distribution of second phase at grain boundaries. TiC particles tended to cluster at grain boundaries as its content exceeded 0.48 wt%, which adversely affected their beneficial effect on the improvement of mechanical properties. At an optimal TiC content of 0.48 wt%, the tensile strength and elongation in the horizontal direction exhibited remarkable enhancements of 27.2% and 319%, respectively, compared to those without the addition TIC particle.

Achieving high-quality joining of silicon carbide (SiC) ceramics and Inconel 718 alloy has become a significant challenge for the brazing process, which is strongly dependent on the filler material. A novel composite interlayer consisting of high-entropy alloys (HEAs), HEA/Ni/HEA, was proposed to reduce the formation of intermetallic compounds in the brazed joints of SiC ceramics and Inconel 718 alloy. A reliable SiC/Inconel 718 brazed joint was produced at 1120 °C for 60 min. The results showed a significant reduction in the number of NiSi compounds in the brazed joint. The brazing seam structure near SiC side was filled with face-centered cubic phases with good plasticity and soft Cu-rich phases due to the high-entropy effect, which effectively suppressed the formation of intermetallic compounds. The maximum shear strength of the brazed joint reached 88 MPa, showing excellent tensile strength. The results provide a valuable basis for improving the joint quality of SiC ceramics and metals by adding high-entropy alloy fillers.

The corrosion behavior of Ti-6Al-2Zr-1Mo-1V (TA15) alloy fabricated through selective laser melting (SLM) technology and traditional wrought technology in hydrochloric acid solutions was investigated using electrochemical testing and surface characterizations, including electron backscattered diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy analyses. The results showed that both types of TA15 alloy underwent spontaneous passivation reactions in HCl solution, and with the increase in HCl concentration, the surface of SLM-TA15 sample exhibited larger and deeper pits. In comparison to SLM-TA15 sample, the pits on the wrought-TA15 sample were shallower and the surface was more uniform. Analysis of the passive current density, breakdown potential, and electrochemical impedance revealed that the corrosion resistance of both alloys decreased as the concentration of HCl increased, and SLM sample exhibited poorer corrosion resistance compared with the wrought sample. Analysis of Mott-Schottky test curves and calculation of passive film thickness indicated that the passive film of wrought-TA15 sample was superior to that of SLM-TA15 sample.

This study investigated the changes in microstructure and mechanical properties of gas tungsten arc welded 7075 aluminum alloy joints using ER5356 and ER7150 filler wire subjected to post-weld heat treatment. The microstructure and mechanical property evolution of the welds was analyzed by both thermodynamics calculations and experimental methods. After welding, alloying elements segregated in the inter-dendritic regions, resulting in the formation of excessive intermetallic compounds. Within the welds of 7075 aluminum alloy with ER5356 filler material, the inter-dendritic region was primarily composed of the T-AlCuMgZn phase. In contrast, in the welds of 7075 aluminum alloy with ER7150 filler material, this region consisted of a eutectic mixture containing α-Al, T-AlCuMgZn, and η-MgZn 2 phases. The α-Al matrix experienced limited supersaturation due to the presence of these inter-dendritic intermetallic compounds, which could not dissolve during the post-weld aging treatment. As a comparison, post-weld solutioning and aging treatment significantly improved the ultimate tensile strength of the joints. Among all the samples, the 7075 + ER7150 sample subjected to post-weld solutioning and aging treatment exhibited the highest strength and elongation, primarily attributed to the complete dissolution of the inter-dendritic intermetallic compounds and the formation of fine precipitates.

Obtaining a fundamental understand of the relationship between weld microstructure and mechanical properties is critical for ensuring a high weld quality. This work explored the micro-mechanism responsible for the mechanical properties of a 10-mm-thickness metastable beta titanium alloy (Ti-3Al-5Mo-4Cr-2Zr-1Fe, wt.%) joint welded by electron beam welding (EBW). Weld microstructure and its evolution behavior were revealed by means of multi-scale microstructure characterization. Obtained results indicate that the absence of alpha phase and formation of nano-scale omega particles occurred in the coarse columnar beta grains of the fusion zone (FZ). Intense dissolution and significant coarsening of secondary alpha phase occurred in the heat affected zone. Between the FZ and HAZ, a partially melted zone was observed and contains few equiaxed beta grains. Compared to the base material, the as-welded EBW joint shows significant softening in weld seam and a slight decrease of 17% in ultimate tensile strength, while a severe reduction of 73% in elongation. It was observed that majority of plastic deformation is confined to the narrow FZ, indicating a significant localization of tensile strain. This leads to premature fracture of the joint within the FZ and consequently to significant deterioration of the overall ductility. This work contributes to advancing the understanding of the role of microstructural evolution on the mechanical properties of high-strength titanium alloy joints via EBW.

The demand for high-quality nickel-titanium (NiTi) shape memory alloy (SMA) and stainless steel (SS) welded structures has led to significant challenges in fusion welding technology, which is largely influenced by filler materials. This study explores the application of CoCrNi medium entropy alloy and CoCrNiFe high entropy alloy as filler materials for laser lap welding of NiTi SMA and 304 SS. A self-fusing joint was produced for comparison. The results demonstrate that the interface zone on the NiTi side was the weakest area regarding cracking defects in NiTi/304 SS lap joints. However, using CoCrNi and CoCrNiFe fillers effectively eliminated cracking defects by considerably suppressing the formation of brittle FeTi and Fe 2 Ti intermetallic compounds (IMCs). The average microhardness value of the weld zone without filler was higher than with CoCrNi and CoCrNiFe. Furthermore, the addition of CoCrNi and CoCrNiFe fillers to NiTi/304 SS lap joints resulted in a substantial increase in tensile properties, with tensile strength reaching 196 ± 39 MPa without filler, 319 ± 25 MPa with CoCrNi, and 377 ± 33 MPa with CoCrNiFe, respectively.

The International Agency for Research on Cancer（IARC） of World Health Organization（WHO） has classified welding fumes as a Group 1 carcinogen to humans. To further understand the rules of welding fume generation, transmission and harm to human body, this paper reviewed the research progress on the welding fumes generation and transmission characteristics of welding fumes and its effect on respiratory system. The effects of welding processes and coating composition of welding consumables on the characteristics of welding fumes were summarized. The influence of diffusion distance on the distribution of welding fumes was emphatically summarized. The effects of size and concentration on the deposition of welding fumes particles were analyzed in detail. Results show that the welding fumes rate and particle size of inert gas shielded welding are larger while tungsten gas shielded welding is opposite. Micro-nano coating on the surface of welding consumables can reduce welding fumes formation rate. With the increase of the diffusion distance, the concentration of welding fumes decreases and the proportion of micro-nano particles increases. When the particle size of welding fumes is less than 2 μm, the particles can be deposited directly in the alveoli, and when the particle size reaches the nanometer level, it can enter the blood circulatory system, thereby affecting people’s physical and mental health.

The increasing demand for achieving high-efficiency and high-quality medium-thick aluminium alloy welded structures, especially for large scale aerospace components, presents an urgent challenge to the conventional TIG arc welding process. This work proposed a novel double-pulsed variable polarity tungsten inert gas (DP-VPTIG) arc, in which the variable polarity square wave current was simultaneously modulated into ultrasonic frequency (20–80 kHz) and low frequency (0.5–10 Hz) pulses. Full penetration welds of 6 mm thick AA2219 aluminum alloy were successfully obtained by using this process. The microstructure and mechanical properties of the weld produced by DP-VPTIG arc were investigated, taking the conventional VPTIG arc as a comparative study. Results show that the microstructure of weld zone by DP-VPTIG arc showed an alternating distribution of fine equiaxed grain band and slightly coarse equiaxed grain band. Compared to VPTIG arc, the grain structure was effectively refined in the weld zone with DP-VPTIG arc, showing a significant reduction of average grain size by 51.2% along transverse section and 61.3% along longitudinal section. The morphology of α-Al+θ-CuAl2 eutectics transformed from continuously distributed netlike shape to separately distributed granular shape, and segregation of Cu solute element was obviously improved. The average microhardness of weld zone was increased by about 8.7% and 5.6% along transverse section and along longitudinal section. The tensile properties of ultimate tensile strength, yield strength and elongation were increased by 6.6%, 10.6% and 20.5%, respectively. The results provide a valuable basis for improving welding efficiency and joint quality through a hybrid pulsed arc.

Aluminum alloy 7075 (with 7055 and 7150 filler wires) was welded using a digital welding machine that can switch arc mode between MIG, CMT and CMT+P modes. The transverse-motion weldability test of joints welded under different arc modes showed that the solidification cracking susceptibility was lower in CMT-technique-based welds than in MIG welds. The temperature cycle of the welding pool under different arc modes was recorded using mini-thermocouples, which showed that the cooling rate was lower in CMT welded samples than in MIG welded samples. The low cooling rate promoted the growth of α-Al dendrites through the back diffusion effect. Electron probe micro-analysis showed that micro-segregation of the α-Al dendrites was lower in the CMT welded samples than in the MIG welded samples. The T-(fAl)1/2 curve of each weld was calculated, which showed that CMT-based welding enhanced the bridging of adjacent α-Al dendrites, reducing the tendency for solidification cracking.

Nano-multilayer films have demonstrated high viability as filler metals for low-temperature bonding applications. This article proposes a novel Cu/W nano-multilayer film as filler material for pulsed pressure diffusion bonding of Ti-6Al-4 V alloy. Cu/W nano-multilayer filler metal with a single layer thickness of 4 μm had a modulation ratio of 1:1. The effect of heating rate on the properties of joints was investigated. The typical joint structure was mainly composed of Ti-6Al-4 V base metal region, CuxTiy intermetallic compound mixed region, and Cu/W elemental region. By increasing the rate of heating, Cu diffused into the Ti-6Al-4 V base metal, reducing the formation of brittle compounds in the bonding and enhancing the tensile strength of the joint. At the heating rate of 30 ℃/s, the tensile strength of joint reached a maximum of 76.7 MPa. Cu/W nano-multilayer film has excellent potential for rapid diffusion bonding application.

The real-time evolution of the deformation and strain field of non-heat-treatable aluminum alloy 5754 and heat-treatable aluminum alloy 6061 resistance spot welding joints during the lap shear test was extracted using the digital image correlation (DIC) technique. The strain competition phenomenon between the nugget and its peripheral metal was quantitatively analyzed by applying 2D and 3D DIC analyses. The quantitative data show the tensile strain concentrated in the peripheral metal of the AA5754-O joint, which fractured in the pull-out mode. In comparison, a significant shear strain appears in the nugget of the AA6061-T6 joint, leading to its fracture in the interfacial failure mode during the lap shear test. The phase evolution of the nugget was analyzed using the thermodynamics database JMatPro, which was further used to calculate the local strength of the joints. The results indicate that the nugget strength of AA5754 is 223 MPa, the nugget strength of AA6061 is 178 MPa, and the heat-affected zone (HAZ) strength of AA6061 is 263 MPa. By inputting the local strength data, the calculated result of the analytical load-bearing competition model is in accordance with the experimental data of the lap shear test.

The influence of filler wire configuration, such as size and geometry, on the deposition rate (DR) and bead formation, has been studied in wire arc-based directed energy deposition (WADED), but the fundamental physics underlying its effect on wire melting and melt pool dynamics remains unclear. In this paper, a series of plasma arc-based DED (plasma-DED) experiments were conducted to investigate the impact of five different filler wire configurations on DR and bead dimensions. The coupling behaviours of wire melting, metal transfer and melt pool dynamics under the five filler wire configurations were also simulated numerically using the authors' recently developed wire-feeding model. The calculated wire melting and bead cross-sections are consistent with the experimental images and measurements. The results demonstrate that the filler wire significantly affects the highest DR by altering wire melting and metal transfer behaviours through changes in arc energy absorption. The filler wire with a rhombus geometry which is closer to a Gaussian-like arc distribution than the flat wire was shown to get higher DR and more stable metal transfer. Furthermore, different filler wire configurations lead to distinct melt pool behaviours, including temperature distribution and flow velocity, due to various metal transfer behaviours and arc shading effects. This study sheds light on the fundamental physics underlying the impact of filler wire on wire melting and bead formation for the first time. The methods and findings can guide improving DR and controlling bead shape in the plasma-DED process.

Enhancement in the mechanical properties of AA2219 Al-6.3Cu(wt.%) alloy arc-welded joints is a guarantee for an excellent service reliability of large aerospace components. This work demonstrates a novel strategy for reinforcing simultaneously in strength and ductility of Al-6.3Cu alloy arc-welded joint enabled by introducing TiC particles (TiCp) embedding into filler wire assisted with a distinctive ultrasonic frequency double-pulsed (UFDP) arc. A fine-formation TiCp/Al-6.3Cu joint characterized by refined alpha-Al equiaxed-grains in welded metal (WM) was successfully fabricated. Undergoing solution and aging treatments, the joint microstructure evolved into a hierarchical alpha-Al grain structure embedded with dense coherent 0"-Al3Cu nano-precipitation (length ~22.3 nm), which consists of refined, mediate-size and coarsen alpha-Al grains in WM, heat-affected zone (HAZ) and base metal (BM), respectively. Relying on a slight grain refinement strengthening and Orowan strengthening in WM, the yield and majority of plastic strain were confined into BM. The as-fabricated TiCp/Al6.3Cu joint exhibited an unprecedented joint coefficient of 93% (UTS 407 MPa) meanwhile an elongation of 16.4%. This work shares an inspiring view on the microstructural design of lightweight alloys arc-welded joint for an outstanding mechanical performance.

设计了三种含量(质量分数)分别为5％、10％和15％的微米氟化物,采用机械涂敷方法在ER5356铝合金焊丝表面制备了氟化物涂层,并与无涂层商用焊丝进行了熔化极气体保护焊(GMAW)工艺性对比.结果表明:微米氟化物涂层铝合金焊丝的焊缝中气孔率显著下降,当涂层中氟化物含量为10％时,焊丝抗气孔性最佳,相比于无涂层的铝合金焊丝,其焊缝气孔率降低约1.6％,接头抗拉强度达到280.79 MPa,提高约2.9％.表面涂敷氟化物涂层的焊丝通过改变电弧形态增加焊缝熔深,从而影响成形外观和力学性能.

Keyhole tungsten inert gas (K-TIG) welding is a variant of TIG welding, which can largely improve the weld penetration depth by forming keyholes inside the molten pool during welding. However, K-TIG welding is generally considered unsuitable for aluminum alloys due to their high thermal conductivity. A novel double-pulsed variable polarity TIG (DP-VPTIG) welding process was employed and the stable full penetration keyhole welding of 7 mm-thick AA2219 aluminum alloy was achieved. Keyhole dynamic evolution for DP-VPTIG was investigated based on visual sensing technology. Results indicate that in low-pulsed peak stage of DP-VPTIG process, the keyhole forms under the dominant role of the downward arc pressure against the upward surface tension and hydrostatic pressure acting on the surface of the molten pool, while the keyhole is closed as the upward surface tension and hydrostatic pressure become the dominant role in low-pulsed base stage. The periodic variation of low-frequency pulse in DP-VPTIG process stimulates a periodic keyhole behavior of "opening" and "closing" in the molten pool. The formation of keyhole is beneficial to the increase of weld penetration depth as the arc moves downwards along the keyhole and directly heats the solid metal under the molten pool. The keyhole size decreases with the increase of low-pulsed frequency.

In the last decade, wire + arc additive manufacturing (WAAM), which is one of the most promising metal additive manufacturing technologies, has been attracting high interest from both academia and industry. WAAM systems are increasingly employed in the industry and academia, but there are still several challenges and barriers to process stability control. The process stability is highly dependent on how the molten feed wire is added into the melt pool, which is known as the droplet transfer mode. To ensure a stable WAAM deposition process, it is essential to maintain the transfer mode in a suitable stable status. Without an effective transfer mode control method, the operators need to determine and control the transfer mode based on their experience using manual adjustment, which is difficult to achieve in a long period of production process. In this paper, a deep learning-based technology was proposed for the control of the droplet transfer mode based on the data collected from the WAAM process. A long short term memory neural network was applied as the core transfer mode classification model. A time-series data, arc voltage, was collected and statistical and frequency features were extracted, which included 11 relevant features, as the inputs of the classification model. Then, the distance between the melted wire and the melt pool was adjusted based on the determined transfer mode to keep a suitable stability of the process. A case study was used to evaluate the proposed approach and to show its merit. The proposed approach was compared to three commonly used machine learning algorithms, k-nearest neighbours, support vector machine, and decision tree. The proposed method obtained the highest accuracy in determining the transfer mode, which was over 91%. The performance of the proposed approach was also evaluated by the single-pass and oscillated wall building. The proposed deep learning based approach improved the process stability in real-time, which resulted in better deposition qualities, in terms of geometry size and processing cleanliness compared to without control. Furthermore, this data-driven method could be applied to other WAAM processes and materials.

铝合金材料具有密度小、比强度高、耐腐蚀性好等特点,是现代社会应用最为广泛的材料之一.纳米陶瓷颗粒具有高强度、高模量、热稳定性好等优点,随着纳米材料技术的不断发展,纳米陶瓷颗粒作为强化材料在铝合金焊接中的应用越来越得到重视.铝合金焊接过程中存在焊缝组织粗化、接头软化和热裂纹等问题,导致铝合金接头在服役过程中失效.纳米颗粒添加入焊缝,具有细化焊缝晶粒、修饰二次相形貌、降低焊接热裂纹、强化焊缝性能的作用,已被用于航空、航天、汽车、高速动车等高强度铝合金的焊接领域.近些年的研究表明,纳米颗粒的含量和成分等物理性质、焊接工艺以及纳米颗粒-基体的界面显著影响焊缝的组织和力学性能.随着纳米颗粒含量增加,焊缝强度显著提高,但是高含量的纳米颗粒容易诱发团聚.不同种类的纳米颗粒能够起到协同强化作用,此外焊接过程中焊接电流、搅拌摩擦参数以及超声和振动等工艺方法可以促使熔池流动提高纳米颗粒在焊缝中的分散程度,从而增强纳米颗粒的强化效果.本文综述了近年来国内外关于纳米陶瓷颗粒在铝合金焊接中的最新研究现状,归纳总结了纳米陶瓷颗粒的物理性质和焊接工艺对复合焊缝强度的影响,重点分析了纳米陶瓷颗粒对焊缝微观组织和热裂纹的影响,介绍了纳米颗粒与基体的界面结合问题,并展望了其未来的研究方向.

Enhancement in the mechanical properties of AA2219 Al-6.3Cu(wt.%) alloy arc-welded joints is a guarantee for an excellent service reliability of large aerospace components. This work demonstrates a novel strategy for reinforcing simultaneously in strength and ductility of Al-6.3Cu alloy arc-welded joint enabled by introducing TiC particles (TiC p ) embedding into filler wire assisted with a distinctive ultrasonic frequency double-pulsed (UFDP) arc. A fine-formation TiC p /Al-6.3Cu joint characterized by refined α -Al equiaxed-grains in welded metal (WM) was successfully fabricated. Undergoing solution and aging treatments, the joint microstructure evolved into a hierarchical α -Al grain structure embedded with dense coherent θ '' -Al 3 Cu nanoprecipitation (length ~22.3 nm), which consists of refined, mediate-size and coarsen α -Al grains in WM, heat-affected zone (HAZ) and base metal (BM), respectively. Relying on a slight grain refinement strengthening and Orowan strengthening in WM, the yield and majority of plastic strain were confined into BM. The as-fabricated TiC p /Al-6.3Cu joint exhibited an unprecedented joint coefficient of 93% (UTS 407 MPa) meanwhile an elongation of 16.4%. This work shares an inspiring view on the microstructural design of lightweight alloys arc-welded joint for an outstanding mechanical performance.