Advances in the Welding of Aluminum Matrix Composites: A New Open Special Issue in Materials

“Advances in the Welding of Aluminum Matrix Composites” is a new open Special Issue of Materials that aims to publish original research and review papers on new scientific and applied research and to make great contributions to advances in the field of welding aluminum matrix composites as well as to the related synthesis, fundamentals, characterization, and application of these materials [...

Microstructure Evolution and Mechanical Properties of 20%SiCp/Al Joint Prepared via Laser Welding

SiC particles-reinforced Al matrix composites (SiCp/AMCs) have been widely used in the aerospace structural components. In this work, 20 vol% SiCp/2A14 joint was fabricated by laser welding technology. The effects of different laser power/welding velocity on the 20 vol% SiCp/2A14 joint forming, microstructure evolution and mechanical properties were studied in detail. The results showed that, under the same heat input, the high power/high welding velocity was beneficial to reduce the porosity of SiCp/2A14 joint and inhibited the formation of brittle phase of Al4C3. At 8 kW-133 mm/s welding parameters, the maximum tensile strength of the SiCp/2A14 joint reached 199 MPa, which is ~64% higher than that of the SiCp/2A14 joint prepared at 4 kW-66 mm/s welding parameters. By analyzing the fracture morphology and SEM image of SiCp/2A14 joint section, it is was found that the porosity of weld and Al4C3 brittle phase were the important factors limiting the strength of SiCp/2A14 joint. This work provides a reference for the process window design of laser welding SiCp/2A14 composites

Effects of solidification on flow dynamics: A novel comprehension of defects formation in laser penetration welding

The laser penetration welding for medium-thickness plates struggles with unstable molten pool behavior and a limited processing window, often leading to welding defects including spatters, depressions, and especially humps. In this study, forming processes of the defects were observed by using a high-speed camera, and forming mechanism of the defects were then analyzed in detail by simultaneously considering the influences of force and solidification. It was clear that the mass loss caused by spattering during the heating phase contributed to the depression, which was consistent with the existing knowledge. However, the formation mechanism of humps concluded in this study was different to the present understanding. Apart from the influences of force, the effects of solidification on molten pools and humps were analyzed. Under the specific conditions, middle part of molten pool solidified rapidly, causing localized necking, and disrupting the circular flow of the molten metal. As a result, molten metal once flowed downward due to the gravity and temperature can no longer refill to the upper part again, leading to the accumulation of molten metal at lower part and ultimately the formation of humps. These findings offered a fresh perspective on the formation of hump, provided valuable guidance for enhancing the quality and efficiency of thick-plate laser welding

Microstructure and mechanical properties of SiCp/Al composite fabricated by concurrent wire-powder feeding laser deposition

In this study, the SiCp/Al matrix composites was fabricated by concurrent wire-powder feeding laser deposition (CWPLD). The microstructure and mechanical properties of the fabricated SiCp/Al composites were studied. The microstructure of fabricated composites consisted of Al matrix, SiC and reaction product Al4C3. The size of α-Al grain (mean area: 275.0 μm2) was much smaller than that of Al specimen fabricated by wire feeding laser deposition (WLD) (mean area: 1544.4 μm2). SiC and Flaky Al4C3 were non-uniformly distributed in the matrix. Al4C3 platelets distributed discontinuously at the interface between unmelted SiC and Al. Due to the inhomogeneous distribution of SiC and Al4C3, the Vickers hardness of the fabricated composites fluctuated violently, ranging from 85 HV to 120 HV. The ductility of the fabricated composites (3.75%) was lower than that of the Al specimen (8.94%) fabricated by WLD. The tensile strength of the fabricated composites (246.0 MPa) was higher than that of the Al specimen fabricated by WLD (230.8 MPa). In the tensile test, only SiC fracture were found in the fracture observation. The bonding strength of interface between SiC and Al was higher than strengths of SiC particle and Al matrix. The debonding between SiC and the Al matrix was not found on the fracture surface of tensile specimens

Study on the effect of ZrC and CNTs particles on Inconel 625 coatings fabricated by coaxial-wire-feed laser cladding

In order to investigate the effect of coaxial-feed laser cladding with the addition of ZrC and CNTs reinforcing particles, a four-split-beam coaxial-wire-feed system was used for the first time to fabricate the cladding layers. Specifically, the effects of the reinforcing particles on the microstructure, mechanical and corrosion properties of the cladding layers were investigated. On 316L substrates, three types of cladding layers were created: pure Inconel 625, Inconel 625 with ZrC, and Inconel 625 with ZrC-CNTs. The testing findings revealed that the cladding layer with reinforcement particles added possessed the ideal geometrical features of large melt width and low dilution rate. Due to the coaxial action of the laser and the wire, the grains on both sides of the single-bead cladding layer transited from columnar crystals to equiaxial crystals along the temperature gradient, and the grains in the middle of the single-bead cladding layer showed the competing growth of columnar crystals and equiaxial crystals at the fusion line. The addition of ZrC and CNTs particles produced a heterogeneous nucleation effect that refined the grain size and homogenized the grain orientation, which CNTs accentuated. Compared with the pure Inconel 625 cladding, the tensile strength of the ZrC/Inconel 625 cladding increased from 731Mpa to 783Mpa, the hardness increased by 29%, and the electrochemical corrosion rate decreased by 53.6%. The elongation of the ZrC-CNTs/Inconel 625 cladding increased from 13.4% to 24%, but the corrosion resistance decreased significantly

Microstructure evolution, interface and mechanical properties of SiCp/2A14 joint during laser keyhole welding

Welding problems have restricted the applications of lightweight SiCp/Al composites in aerospace. In this work, the controllability of the keyhole mode, nucleation mechanism, and mechanical properties of the laser-welding process are studied in detail. The extrusion effect formed by the open keyhole pushes SiC particles to the bottom of the molten pool. To observe the nucleation and growth mechanism of the Al4C3 of keyhole laser-welded SiC/2A14Al composites, the dissolution–precipitation behavior of the SiC particles and growth behavior of the Al4C3 tip were observed. Owing to its high chemical properties, Al4C3 mainly begins nucleating from the open edges of the SiC particles and its formation is mainly distributed along the direction of Al grains. Al4C3 was the main crack source and propagation path while the small-sized SiC particles hindered the crack propagation. This work innovatively regulates the keyhole mode to achieve ‘small damage breakdown’ laser welding, greatly reducing the volume fraction of Al4C3. It also provides new insight into fusion welding of SiC particle-reinforced Al matrix composites

Silicon nitride assisted carbon nanotubes induced stacking faults and twins in aluminum alloy composite joint

The extensive heat input during welding can generally disrupt the meticulously crafted microstructure of the Al alloy substrate, leading to a marked decrease in the mechanical performance of the traditional joint. Here, we conducted a study of adding silicon nitride and CNTs to form Al composite joints, which not only compensated for the microstructural defects caused by welding, but also improved the tensile strength of the joints by 31%. Importantly, microstructural analysis reveals that there are twinning and SFs in both Al and Al4C3 phase. It was contributed to Al4C3 growth and the reduction in Al alloy SFs energy by CNTs. Moreover, the residual CNTs and Al4C3 phase in the composite joints refined the original precipitation phase network. This work is supposed to provide new insights into the strengthening of composite joints based on SFs and twins

Microstructure and properties of Al–Cu–Mg alloy welded by 14 μm single-mode laser small oscillation welding

In this paper, the 14 μm single-mode laser oscillation welding technique was adopted to achieve high-quality welding of 2A12 aluminum alloy. Specifically, its influence on the microstructure and mechanical properties of the joint and the formation mechanism were investigated. The results showed that the ultra-small spot laser (28 μm) was able to achieve sequential oscillation of the molten pool with small amplitude (0.1 mm). The increased frequency caused the average grain size to decrease and the grain boundary length increased in the fusion zone. Meanwhile, the average grain orientation difference increased, and the growth orientation was more dispersed and homogeneous. While reducing weld morphology defects and refining grain microstructure, there was little influence on the penetration and width morphology of the weld. Finally, successfully prepared welds with tensile strength up to 410.4 MPa and elongation simultaneously increased to 4.065 % at 200 Hz. Furthermore, the influence of keyhole oscillation on the molten pool flow at small amplitude was explained by high-speed camera observation, which explored the mechanism of grain growth in the oscillating joints and provided new ideas for the welding of 2xx aluminum alloys