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A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Welding and Joining".

Deadline for manuscript submissions: closed (31 May 2023) | Viewed by 21358

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Prof. Dr. Xiangdong Gao

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Guest Editor

Guangdong Provincial Welding Engineering Technology Research Center, Guangdong University of Technology, Guangzhou 510006, China
Interests: laser beam welding; laser–arc hybrid welding; seam tracking; monitoring of laser/arc welding; laser welding of dissimilar materials; numerical simulation of laser welding process; weld nondestructive testing

Special Issue Information

Dear Colleagues,

Laser welding of metals is an important technology. The advantages, such as high welding speed, high productivity, and high concentration of energy, have made laser welding attractive in many industrial applications. In reality, the joining of same or dissimilar metals together using laser welding is an extremely complicated process, which contains a large number of physical and metallurgical effects. Improvement of laser welding product quality relies on an increased understanding of laser welding process and the ways in which this process can be monitored and controlled by advanced techniques. In addition, with synergistic action of the laser beam and welding arc, laser–arc hybrid welding is also an attractive technique which offers many advantages, such as good gap bridging ability, deep penetration, high welding speed, as well as better welding process stability and efficiency.

Articles focusing on the review, investigation, and innovations of laser welding and laser-arc hybrid welding of the same or dissimilar metals are all welcome to this Special Issue of Metals. Research on seam tracking, welding process monitoring, and diagnosis based on optical, plasma, vision, and acoustical sensors, dynamic modeling of welding process, advanced control of laser welding process, numerical analysis of laser welding processes and structures, and optimal design of laser welding processes will be expected in this Special Issue. A discussion of the properties of laser weld pool, keyhole, heat transfer during laser welding, microstructure, metallurgical and mechanical properties of laser weld will be covered. Additionally, nondestructive testing for laser welding products, and intelligent methods of weld defect detection with machine learning and signal processing related to laser welding or laser–arc hybrid welding are encouraged for submission. Experimental studies and simulations of laser welding and laser-arc hybrid welding, as well as industrial applications, are of interest in this Special Issue.

Prof. Dr. Xiangdong Gao
Guest Editor

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Keywords

laser beam welding
laser–arc hybrid welding
seam tracking
monitoring of laser welding
laser welding of dissimilar materials
simulation of laser welding process
laser weld nondestructive testing
analysis of laser weld microstructure
metallurgical and mechanical properties of laser welding metals
weld formation

Published Papers (12 papers)

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Research

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12 pages, 6301 KiB

Open AccessArticle

Effect of Beam Oscillation Amplitude on Microstructure and Mechanical Properties of Small Laser Spot Welded QP980 Steel

by Jingwei Yang, Tao Li, Wolin Ye, Jiale Chen and Jian Qiao

Metals 2023, 13(8), 1363; https://doi.org/10.3390/met13081363 - 28 Jul 2023

Viewed by 802

Abstract

In this study, butt welds of QP980 steel were produced using small laser spot (0.1 mm) oscillating welding. The effect of beam oscillation with a circular trajectory on weld morphologies, microstructures, and mechanical properties was characterized. As the oscillating amplitude rose, the energy accumulation range enlarged, and the energy peak value was decreased, leading to the appearance of the cross-section changing from a nail-like shape to a cup-cone-like shape and then to a W-type shape. The weld zone is divided into the fusion zone, inner heat-affected zone, and outer soften zone. The fusion zone and inner heat-affected zone are full of typical lath martensite and have the highest hardness. The soften zone is composed of pre-existing martensite, temper martensite, ferrite, and retained austenite and has the lowest hardness. Compared to laser welding, beam oscillation could reduce the pre-existing block martensite to decompose, leading to a narrower width and higher hardness soften zone. Although the width of the fusion zone and soften zone increases with the oscillation amplitude, all welded samples failed at the base metal with 97% joint efficiency. Full article

(This article belongs to the Special Issue Laser Welding Technology)

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20 pages, 9251 KiB

Open AccessArticle

Study on Laser Overlap Welding of Titanium/Aluminum Dissimilar Metals Based on Niobium Microalloying

by Hao Pan, Yue Wang, Shaoning Geng, Annan Yin, Chu Han and Jintian Zhao

Metals 2023, 13(7), 1257; https://doi.org/10.3390/met13071257 - 11 Jul 2023

Cited by 1 | Viewed by 1068

Abstract

Brittle intermetallic compounds, formed during the welding process of titanium/aluminum (Ti/Al), lead to a significant reduction in joint mechanical properties. The purpose of this study is to mitigate the formation of brittle phases during the laser welding of dissimilar Ti/Al metals, thereby enhancing the mechanical properties of the joints. In this investigation, an innovative approach is adopted, utilizing Nb foil as an interlayer to effectively minimize the formation of brittle intermetallic phases during dissimilar welding. A comprehensive analysis of the microstructure of the transition layer was conducted using material characterization methods, including scanning electron microscope equipped with an energy dispersive X-ray spectrometer. The mechanical performance of the welded joints was assessed using tensile testing. The results indicate that the effective welding width and joint penetration depth at the joint interface were reduced in Ti/Al dissimilar metals when Nb was added as an intermediate layer, under the same welding process parameters, when compared to unalloyed weld seams. Furthermore, the utilization of a 0.05 mm Nb foil as the intermediate layer results in a significant 25% increase in the average shear strength compared to the other condition, with the average shear strength of the joint reaching its peak value at 192 N/mm. The unalloyed Ti/Al weld joint usually fractured along the melting zone, displaying complete brittle fracture characteristics. After Nb microalloying, the joint typically fractures along the transition zone and interface, exhibiting both cleavage and ductile fracture characteristics, indicating the combination of a brittle and toughness fracture. This study provides experimental evidence and new insights for welding Ti/Al composite structures, with significant theoretical and practical applications. Full article

(This article belongs to the Special Issue Laser Welding Technology)

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31 pages, 8462 KiB

Open AccessArticle

Laser Weld Aspect Optimization of Thin AISI 316 SS Using RSM in Relation with Welding Parameters and Sulfur Content

by Kamel Touileb, Elawady Attia, Rachid Djoudjou, Abdallah Benselama, Albaijan Ibrahim, Sahbi Boubaker, Jose Ponnore and Mohamed M. Z. Ahmed

Metals 2023, 13(7), 1202; https://doi.org/10.3390/met13071202 - 28 Jun 2023

Cited by 1 | Viewed by 1040

Abstract

A quantitative and qualitative study of the effect of laser (light amplification by stimulated emissions of radiation) welding parameters, such as focus point, welding speed, power beam and shield gas on bead profile in relation with microchemistry compositions differences of two thin AISI 316 industrial stainless steel casts have been studied. One cast contains 60 ppm (0.006%) of sulfur considered as high sulfur content and the other one contains 10 ppm (0.001 %) sulfur which can be considered as low sulfur content. A set of 27 tests were carried out by combining three welding speeds (1500, 3000, and 4500 mm/min), three shield gases (helium (He), mixture of 40% helium and 60% argon (Ar) and mixture of 70% helium and 30% argon) with flow rate of 15 L/min, and three focal lengths (+2, +7, and +12 mm). The depth, aspect ratio (the ratio between the penetration depth weld and the weld width) and the bead cross section profile are investigated using response surface methodology (RSM). Linear and quadratic polynomial models for predicting the weld bead geometry were developed. The results of the preliminary validation indicated that the proposed models predict the responses adequately. The geometry of the welded area was analyzed using optical microscopy, and correlations between weld morphology (depth, weld aspect parameter and weld area) and welding parameters were performed. For the cast 316 HS (high sulfur content), the main input factor influencing the depth weld (Y_d) is the focus point with a contribution up to 19.32. On the other hand, the main input factor affecting the depth weld (Y_d) of the cast 316 LS (low sulfur content) is the combination effect of focus point and power input energy with contribution up to 10.65%. Sulfur as the surfactant element contributes to determining the laser weld bead shape up to 71% when the welds are partially penetrated and diminishes to 50% when the welds are fully penetrated with the occurrence of the keyhole mechanism. Full article

(This article belongs to the Special Issue Laser Welding Technology)

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13 pages, 5076 KiB

Open AccessArticle

Microstructure of Butt Joint of High-Silicon Steel Made Using CO₂ Laser Welding and Inconel 82 Filler

by Ming-Feng Chiang, Ping-Hui Chien, Tzu-Yuan Lo and Ren-Kae Shiue

Metals 2023, 13(2), 234; https://doi.org/10.3390/met13020234 - 26 Jan 2023

Viewed by 1207

Abstract

A nickel-based filler wire, Inconel 82, was applied to weld a high-silicon steel plate with a chemical composition in wt% of 2.6 Si, 0.5 Al and Fe balance. The chemical composition of the heterogeneous weld bead was deviated from that of the conventional alloy due to incomplete mixing/convection between the filler wire and base metal in the weld pool. The microstructure of the weld bead was examined in greater depth by FESEM/EBSD, EPMA/WDS and STEM/EDS in the experiment. The heterogeneous weld bead was primarily composed of austenite and martensite, and mainly governed by the Ni concentration. A Schaeffler diagram based on the ratio of Cr and Ni equivalents in the selected positions of the weld bead was used to predict the structure and phase(s) of the Fe-based weld bead. A methodology for the analysis of a weld metal with an unconventional alloy composition has been proposed in the study. Full article

(This article belongs to the Special Issue Laser Welding Technology)

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16 pages, 5443 KiB

Open AccessArticle

Optimization of Response Surface Methodology for Pulsed Laser Welding of 316L Stainless Steel to Polylactic Acid

by Jiakai Wu, Perry P. Gao and Xiangdong Gao

Metals 2023, 13(2), 214; https://doi.org/10.3390/met13020214 - 22 Jan 2023

Cited by 2 | Viewed by 1397

Abstract

A laser welding technology for the dissimilar materials 316L stainless steel (316L ss) and polylactic acid (PLA) was investigated to analyze the process parameters, which have a large influence on the joint quality. Orthogonal tests, single-factor tests, response surface method (RSM), and Box–Behnken design (BBD) were utilized to optimize the experimental design. A metallographic microscopy analysis was conducted to classify the joint morphology into two categories: effective and ineffective. The effective area ratio was established as an effective judgment method for the joint mechanical properties. Mathematical relations between the process parameters and the mechanical properties of the joints were investigated and the process parameters were optimized and validated. The test values were in excellent agreement with the actual values, thus demonstrating the reliability of the proposed model. Full article

(This article belongs to the Special Issue Laser Welding Technology)

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12 pages, 4687 KiB

Open AccessArticle

Welding Properties of Dissimilar Al-Cu Thin Plate by a Single-Mode Fiber Laser

by Soon-Jae Lee, Kwang-Deok Choi, Su-Jin Lee, Dong-Sik Shin and Jae-Pil Jung

Metals 2022, 12(11), 1957; https://doi.org/10.3390/met12111957 - 15 Nov 2022

Cited by 4 | Viewed by 1418

Abstract

To improve the reliability and safety of the electrical components used in automobiles, Cu and Al have recently been employed as electrodes, wherein lasers were used for rapid welding. However, in Al-Cu dissimilar metal welding, intermetallic compounds (IMCs) reduce the weld strength. In addition, the laser absorption rates of Al and Cu are low, and the reflectance is high, thereby impeding the welding process. To increase the absorption rate, a laser with a high beam quality must be used. Thus, a high-density, high-quality 5 kW single-mode laser was employed. Thin Al and Cu (0.2 mm thick) plates were processed and welded at welding speed 200–1000 mm/s, changing the laser-irradiated upper metal to Cu or Al. Post analysis, it was found that with a high heat input, pores were generated inside the Al, and when the upper metal was Cu, pores were mainly generated between the Al molten layer and the Cu mixed layer. As a result of tensile shear strength measurement, most of the aluminum area fractured at 118–151 N, and when fractured in copper, the strength was highest at 154 N. At a high welding speed, fracture was mainly observed at the joints along the IMCs or in the Cu mixed layer. Full article

(This article belongs to the Special Issue Laser Welding Technology)

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14 pages, 23576 KiB

Open AccessArticle

Relationship between Microstructure and Corrodibility of Local Dry Underwater Laser Welded 304 Stainless Steel

by Danbi Song, Jungsoo Choi, Dongsig Shin and Su-Jin Lee

Metals 2022, 12(11), 1904; https://doi.org/10.3390/met12111904 - 7 Nov 2022

Cited by 2 | Viewed by 1716

Abstract

To understand the relationship between microstructure and corrosion, in this study, underwater bead-on-plate laser welding was compared with the in-air laser welding of 10-mm-thick 304 stainless steel plates at different laser powers (2, 4, and 6 kW). Welding was performed via local dry underwater laser welding (UWLW) using a custom-designed nozzle and a fiber laser at a water depth of 70 mm. The best weld quality was obtained in both underwater and in-air environments using 2 kW of laser power. To understand the relationship between the microstructure and corrosion resistance of 304ss in underwater laser welding (UWLW), this study was conducted using a custom-designed nozzle. The grain boundary analysis revealed that the specimen prepared by UWLW had high-angle grain boundaries content approximately 1.5 times higher than that of the specimen produced by in-air laser welding, and the fraction of the coincidence site lattice (CSL) boundaries was increased remarkably. High residual stress and microchromium precipitation were observed in the UWLW specimen, and the corrosion rate of the same at 2 kW laser power was considerably similar to that of the in-air laser weld specimen. Full article

(This article belongs to the Special Issue Laser Welding Technology)

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13 pages, 11661 KiB

Open AccessArticle

Effect of Alternating Magnetic Field on Arc Plasma Characteristics and Droplet Transfer during Narrow Gap Laser-MIG Hybrid Welding

by Baihao Cai, Juan Fu, Yong Zhao, Fugang Chen, Yonghui Qin and Shuming Song

Metals 2021, 11(11), 1712; https://doi.org/10.3390/met11111712 - 27 Oct 2021

Cited by 11 | Viewed by 2086

Abstract

In this paper, the morphological characteristics of arc plasma and droplet transfer during the alternating magnetic field-assisted narrow gap groove laser-MIG (metal inert gas) hybrid welding process were investigated. The characteristics of arc plasma and droplet transfer, electron temperature, and density were analyzed using a high-speed camera and spectrum diagnosis. Our results revealed that the arc maintained a relatively stable state and rotated at a high speed to enhance the arc stiffness, and further improved the stability of the arc under the alternating magnetic field. The optimum magnetic field parameters in this experiment were B = 16 mT and f = 20 Hz, the electron temperature was 9893.6 K and the electron density was 0.99 × 10¹⁷ cm⁻³ near the bottom of the groove, which improved the temperature distribution inside the narrow gap groove and eliminated the lack of sidewall fusion defect. Compared to those without a magnetic field, the magnetic field could promote droplet transfer, the droplet diameter decreased by 17.6%, and the transition frequency increased by 23.5% (owing to the centrifugal force during droplet spinning and electromagnetic contraction force). The width of the weld bead was increased by 12.4% and the pores were also significantly reduced due to the stirring of the magnetic field on the molten pool. Full article

(This article belongs to the Special Issue Laser Welding Technology)

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17 pages, 11665 KiB

Open AccessArticle

Droplet Transfer Induced Keyhole Fluctuation and Its Influence Regulation on Porosity Rate during Hybrid Laser Arc Welding of Aluminum Alloys

by Leilei Wang, Yanqiu Zhao, Yue Li and Xiaohong Zhan

Metals 2021, 11(10), 1510; https://doi.org/10.3390/met11101510 - 23 Sep 2021

Cited by 5 | Viewed by 1910

Abstract

Hybrid laser arc welding (HLAW) features advantages such as higher welding speed and gap tolerance as well as smaller welding deformation and heat-affected zone than arc welding. Porosity in hybrid laser arc weld due to keyhole fluctuation tends to be the initial source of crack propagation, which will significantly diminish the weld performance. A high-speed imaging technique was adopted to record and analyze the droplet transfer and keyhole fluctuation behavior during hybrid laser arc welding of aluminum alloys. A heat transfer and fluid flow model of HLAW was established and validated for a perspective of the evolution process of droplet transfer and keyhole fluctuation. The relationship between keyhole fluctuation and weld porosity was also revealed. During the droplet transfer stage, liquid metal on the top surface of the weld pool flows toward the keyhole originated by globular transfer, and the keyhole fluctuates and decreases significantly, which has a higher tendency to form a bubble in the weld pool. The bubble evolves into porosity once trapped in the mush-zone near the trailing edge of the weld pool. Therefore, globular transfer during HLAW is the principal origin of keyhole fluctuation and weld porosity. Welding current has a significant influence on keyhole fluctuation and weld porosity rate. Droplet transfer frequency, keyhole fluctuation, and porosity rate increase with higher welding current under the globular transfer mode. The porosity rate shows a nearly positive correlation with the standard deviation of keyhole fluctuation. Full article

(This article belongs to the Special Issue Laser Welding Technology)

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18 pages, 7828 KiB

Open AccessArticle

Interface Formation and Bonding Mechanisms of Laser Welding of PMMA Plastic and 304 Austenitic Stainless Steel

by Yijie Huang, Xiangdong Gao, Bo Ma and Yanxi Zhang

Metals 2021, 11(9), 1495; https://doi.org/10.3390/met11091495 - 21 Sep 2021

Cited by 13 | Viewed by 2535

Abstract

Laser welding experiments involving amorphous thermoplastic polymer (PMMA) and 304 austenitic stainless steel plates were conducted to explore the influence of laser welding process parameters on plastic–metal joints. A high-speed camera was applied to record the dynamics of the molten pool and the formation of bubbles to reveal the bonding mechanisms of the hybrid joints. The influence of process parameters on the joints was analyzed using temperature measurements performed with thermocouples. The microstructure morphology of joints was observed using SEM. The mechanical characterization of the hybrid joints was carried out to understand the effect of the welding conditions on the weld morphology, flaws and shear stress. Different interface temperatures resulted in two types of bubbles and led to different weld morphology characteristics. A stable hybrid joint with the best shear stress was produced with a laser line energy of 20.16 J/mm², a temperature of 305 °C and small bubbles. The shear stress of the effective joint under the maximum mechanical resistance was 4.17 MPa. The chemical bonds (M-O, M-C) and mechanical anchoring that formed on the steel’s surface contributed to the joint bonding. Range analysis provided guidance for identifying the impact of individual factors in the shear stress for the laser welding of plastic–metal. Full article

(This article belongs to the Special Issue Laser Welding Technology)

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13 pages, 6304 KiB

Open AccessArticle

Interfacial Microstructure and Formation of Direct Laser Welded CFRP/Ti-6Al-4V Joint

by Pengyuan Zou, Hua Zhang, Min Lei, Donghai Cheng, Shuo Huang and Fan Yang

Metals 2021, 11(9), 1398; https://doi.org/10.3390/met11091398 - 3 Sep 2021

Cited by 11 | Viewed by 1838

Abstract

Joining fiber reinforced polyether ether ketone resin matrix composite (PEEK-CFRP) with Ti-6Al-4V titanium alloy to form a composite structure is a promising manufacturing process. Huge difference of material properties is the biggies challenge to join them. Continuous laser welding process is conducted in this experiment to join the two materials. In this study, joints under different welding speeds were obtained. Mechanical properties and microstructures were observed, and the interfacial structures were tested. The results showed that fixed joint could be obtained. As the welding speed decreased, the tensile shear first increased and then decreased. The shear force reached a maximum value of 36.8 N/mm at the speed of 10 mm/s. The quality of joint could be observably affected by welding speed. The formation of bubbles, cracks, and anchor effect at the interface were the main factors affecting the mechanical property of joint. Thus, adhesion failure was the main failure form for CFRP fracture. Ti, Al and some other elements had been diffused across the interface, resulting in the formation of intermediate transition layer. The result of EDS, X-ray and XPS test indicated that CTi_0.42V_1.58 phase could be formed, and Ti at the interface could react with the oxygen and carbon of CFRP to form TiO₂, TiO and TiC, forming a stable joint structure. Full article

(This article belongs to the Special Issue Laser Welding Technology)

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Review

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41 pages, 7925 KiB

Open AccessReview

Research Progress on Characterization and Regulation of Forming Quality in Laser Joining of Metal and Polymer, and Development Trends of Lightweight Automotive Applications

by Zhenhong Zhou, Xiangdong Gao and Yanxi Zhang

Metals 2022, 12(10), 1666; https://doi.org/10.3390/met12101666 - 4 Oct 2022

Cited by 12 | Viewed by 2393

Abstract

Metal–polymer hybrid structures have been widely used in research into their lightweight automotive applications, because of their excellent comprehensive properties. As an efficient technology for automatic connection of dissimilar materials, laser joining has great application potential and development value in the field of lightweight automotive design. However, due to the physical and chemical differences between metals and polymers, the formation quality of the hybrid joint is seriously affected by defects, low bonding strength, and poor morphology. Meanwhile, it is difficult to meet the demands for lightweight automobiles by considering only bonding strength as the target for forming quality. Therefore, the technological characteristics of metal–polymer hybrid structures for use in lightweight automotive applications are analyzed, the advantages and problems of laser-joining technology are discussed, and the characterization indexes and regulation measures of forming quality in laser joining are summarized. This paper which provides reference and guidance for reliable forming, intelligent development, and lightweight application of laser joining for polymer–metal hybrid structures. Full article

(This article belongs to the Special Issue Laser Welding Technology)

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