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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 (28 February 2023) | Viewed by 22761

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Dr. Pasquale Russo Spena

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Guest Editor

Department of Management and Production Engineering, Politecnico di Torino, 10129 Torino, Italy
Interests: welding processes; mechanical joining; automotive metals; mechanical testing; microstructural examination
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

A large number of research activities concerning the welding of metal alloys are ongoing in many industrial fields. The ability to effectively weld traditional and innovative metals is mainly driven by the metallurgical phenomena that are involved in the joining process. These are not fixed factors for a given metal but also depend on joint shape and welding techniques.

Therefore, an understanding of welding metallurgy and of the influence of the welding processes on weld microstructure, mechanical properties, and appearance (e.g., defects, distortions due to residual stresses) is crucial to guarantee the performance of assembled parts and structures during the service, in any field.

This Special Issue aims to collect the most recent research on innovative and pioneering works in welding metallurgy that cover several aspects such as microstructure–property relationships of welds, welding techniques (fusion welding and solid-state welding), residual stress and distortion, post-weld heat treatment, numerical simulation of weld solidification and cooling, as well as corrosion phenomena.

Dr. Pasquale Russo Spena
Guest Editor

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Keywords

welding metallurgy
weldability
ferrous and non-ferrous alloys
fusion welding
solid-state welding
microstructure–mechanical property relationships
residual stress and distortion
post-weld heat treatment
modeling and FEM simulation
corrosion

Published Papers (10 papers)

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Research

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11 pages, 12225 KiB

Open AccessArticle

Role of Carbon Content on Microstructure Evolution and Impact Toughness in Coarse-Grained Heat-Affected Zone of High-Strength Steel

by Xuelin Wang, Zhenjia Xie, Wenjuan Su and Chengjia Shang

Metals 2023, 13(1), 106; https://doi.org/10.3390/met13010106 - 4 Jan 2023

Cited by 1 | Viewed by 1508

Abstract

The effect of carbon content in the base metals of high-strength steel on the microstructure and impact toughness of simulated welding focusing on a coarse-grained heat-affected zone (CGHAZ) at different heat inputs was systematically investigated by using scanning electron microscopy (SEM) and electron back-scattering diffraction (EBSD). The Charpy impact test confirmed that there was an optimal heat input, which caused the CGHAZ to obtain the highest impact toughness. The optimal heat input is ~20 kJ/cm and remains unchanged with an increase in carbon content from 0.04 to 0.12 wt.%. However, the impact toughness of the CGHAZ decreases with the increase in carbon content at each heat input. Microstructure characterization showed that a CGHAZ with 0.04 wt.% carbon gradually changed from lath bainite (LB) to granular bainite (GB) with an increase in heat input, while it changed from lath martensite (LM) to LB and then to GB for a CGHAZ with 0.12 wt.% carbon. Although the density of high-angle grain boundaries (HAGBs) obtained at 20 kJ/cm in the high-carbon sample is higher than that of the low-carbon sample, its impact toughness is lower, which is related to the parallel structure of the lath bundles and the morphology the austenite penetration. Full article

(This article belongs to the Special Issue Welding Metallurgy)

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12 pages, 4900 KiB

Open AccessArticle

Effect of Hybrid Laser Arc Welding on the Microstructure and Mechanical and Fracture Properties of 316L Sheet Welded Joints

by Linyi Xie, Wenqing Shi, Teng Wu, Meimei Gong, Detao Cai, Shanguo Han and Kuanfang He

Metals 2022, 12(12), 2181; https://doi.org/10.3390/met12122181 - 18 Dec 2022

Cited by 1 | Viewed by 1288

Abstract

To explore the influence of different welding modes on the properties of 316L thin-plate welded joints, a new type of laser arc compound gun head similar to a coaxial one was used in this experiment. A high-speed camera was used to record the welding process and analyze the droplet splash behavior of the molten pool. The microstructure, microhardness change, and tensile test results of welded joints under different welding modes were analyzed. The results showed that laser welding (LW) is more prone to molten pool splash than hybrid laser arc welding (HLAW). The HLAW pool area was significantly increased compared with that of LW. The HLAW joint microstructure was more uniform than that of LW, which can improve the microhardness of welded joints. HLAW improved the tensile properties of the joint, with the maximum tensile strength of the joint increasing from 433 to 533 MPa. This test can provide guidance for the HLAW process. Full article

(This article belongs to the Special Issue Welding Metallurgy)

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11 pages, 3709 KiB

Open AccessArticle

Investigation of Strength and Formability of 6016 Aluminum Tailor Welded Blanks

by Dario Basile, Raffaella Sesana, Manuela De Maddis, Luca Borella and Pasquale Russo Spena

Metals 2022, 12(10), 1593; https://doi.org/10.3390/met12101593 - 24 Sep 2022

Cited by 1 | Viewed by 1847

Abstract

The automotive industry is constantly looking for innovative techniques to produce lighter, more efficient, and less polluting vehicles to comply with the increasingly restrictive environmental regulations. One of the latest technologies, which is still developing, is based on the fabrication of the body-in-white and car parts through the stamping of aluminum tailor welded blanks. Tailor welded blanks (TWBs) are generally a combination of two/three metal sheets with different thicknesses and/or mechanical strengths, which are commonly laser butt-welded. Even though the aluminum TWBs have the main advantage of producing lightweight parts, their use is still limited by the lower formability than their parent materials and by the fact that laser welding of aluminum sheets still remains a process easily subjected to weld defects (i.e., internal porosity) and, hence, requires strict control of process parameters. This study has investigated the effects of the main laser welding process parameters (laser power, welding speed, and focus position) on the mechanical properties and formability of aluminum TWBs made of the 6xxx series. The research results show that the welding conditions highly influence the weldability of such alloys. Heat input over 70 J/mm is responsible for excessive porosity and molten pool (and consequent root concavity), which are responsible for the lowest mechanical strength and formability of joints. Differently, low amounts of imperfections have a limited influence on the mechanical behaviors of the TWB joints. Overall, a narrow weldability window is required to ensure welded joints with proper strength and limited or no porosity. Full article

(This article belongs to the Special Issue Welding Metallurgy)

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20 pages, 23599 KiB

Open AccessArticle

A Study on the Development of an Optimization Algorithm and Determination Procedure for Toughness Deterioration Characteristics through Flux Core Arc Heat Input Control of ASTM A553-1 (9% Nickel Steel)

by Minho Park, Jaewoong Kim and Changmin Pyo

Metals 2022, 12(7), 1213; https://doi.org/10.3390/met12071213 - 18 Jul 2022

Cited by 1 | Viewed by 1390

Abstract

The International Maritime Organization has adopted the reduction of carbon dioxide emissions from ships as an important priority, and is continuously strengthening its regulations on marine air pollution. By 2035, it is expected that LNG-powered ships will account for more than 50% of the available ships. Accordingly, the demand for equipment related to LNG-fueled ships is expected to grow as well, requiring the development of a lot of equipment. However, the characteristics of LNG-powered ships mean that they require a high level of reliability and long history of operating reliably. Even when a product is developed, numerous demonstrations and quality assurance measures are needed to reach the technological level ship owners and customers require. Therefore, an optimization procedure to determine the welding quality for 9% Ni steel is necessary. In this study, the heat input criteria that induce brittle fracture characteristics were analyzed to optimize the flux core arc welding process for 9% Ni steel used in the manufacture of LNG storage tanks. We developed an optimization algorithm (Welding Current, Arc Voltage, Welding Speed) that can select a group of fracture conditions by examining the tendency of the tissue to brittle fracture due to excessive heat input among potential quality issues of cryogenic steel. Capable of selecting the range in which quality deterioration occurs, determining quality of a weld and avoiding the range in which toughness degradation occurs, through which a process to derive high quality 9% Ni welds is proposed. Full article

(This article belongs to the Special Issue Welding Metallurgy)

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18 pages, 2138 KiB

Open AccessArticle

A Study on Heat Input Control and a Quality Evaluation Algorithm to Prevent Toughness Deterioration of the Heat-Affected Zone in the Fiber Laser Welding Process of ASTM A553-1 (9% Nickel Steel) Material

by Minho Park, Jaewoong Kim and Changmin Pyo

Metals 2022, 12(7), 1195; https://doi.org/10.3390/met12071195 - 13 Jul 2022

Cited by 2 | Viewed by 1428

Abstract

Various international organizations and governments of many countries are making efforts to prevent environmental pollution, with the IMO (International Maritime Organization) reinforcing related regulations. With these regulations, equipment related to LNG-fueled ships, which have the greatest carbon dioxide reduction effect among eco-friendly ships, are expected to increase. Although the IGC code designates the materials that can be used for LNG containers, such as 304L stainless steel and 9% nickel steel, these materials have a tendency to deteriorate the tissue around the heat-affected zone due to excessive heat input. In this study, we analyzed the effect of brittle fracture in the weld zone and heat-affected zone after fiber laser welding and found that welding quality improved with control of the heat input. SVM discriminant analysis was applied to classify the groups in which brittle fracture and ductile fracture occurred. The shape of the penetration section, hardness in the welding zone and heat-affected zone, and fracture surface were selected as factors for discrimination; these values were determined under various welding conditions. With these data, we derived a regression model and multi-objective optimization algorithm to predict mechanical properties after welding, as well as the conditions necessary to prevent brittle fracture. Finally, the prediction models were verified, as the results of welding under the derived conditions were classified as ductile fracture group. Full article

(This article belongs to the Special Issue Welding Metallurgy)

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18 pages, 5428 KiB

Open AccessFeature PaperArticle

A Study on Determining Weld Joint Hardening and a Quality Evaluation Algorithm for 9% Nickel Weld Joints Using the Dilution Ratio of the Base Material in Fiber Laser Welding

by Minho Park, Jisun Kim, Changmin Pyo, Jaewoong Kim and Kwangsan Chun

Metals 2021, 11(8), 1308; https://doi.org/10.3390/met11081308 - 18 Aug 2021

Cited by 1 | Viewed by 1850

Abstract

The demand for LNG-powered ships and related equipment is rapidly increasing among major domestic and foreign carriers due to the strengthened IMO regulations on the sulfur content of ship fuel oil. LNG operation in a cryogenic environment requires a storage tank and fuel supply system that uses steel with excellent brittleness and fatigue strength. A ship using LNG is very sensitive to explosion and fire. For this reason, 9% Ni is often used, because ships require high quality products with special materials and structural technologies that ensure operability at cryogenic temperatures. However, research to derive uniform welding quality is urgent because the deterioration of weld quality in the 9% Ni steel welding process is caused by high process difficulty and differences in welding quality depending on a welder’s skill set. This study proposes a method to guarantee a uniform quality of 9% Ni steel in a fiber laser welding process by categorizing weld joint hardness according to the dilution ratio of a base material and establishing a standard for quantitative evaluation. Full article

(This article belongs to the Special Issue Welding Metallurgy)

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18 pages, 6143 KiB

Open AccessFeature PaperArticle

A Study on the Weldment Hardening Discrimination Procedure and Improvement of Flux Cored Arc Welding Process of ASTM A553-1 (9% Nickel Steel) Material Using Bead Geometry Distribution

by Minho Park, Jisun Kim, Changmin Pyo, Jaewoong Kim and Kwangsan Chun

Metals 2021, 11(8), 1282; https://doi.org/10.3390/met11081282 - 13 Aug 2021

Cited by 2 | Viewed by 1750

Abstract

As a result of strengthened sulfur content standards for ship fuel oil in IMO regulations, major domestic and foreign carriers have a high and growing demand for liquefied natural gas (LNG) powered ships and related equipment. For LNG operation in a cryogenic environment, a storage tank and fuel supply system that uses steel with excellent brittleness and fatigue strength is required. Ships that use LNG have a high vulnerability to explosion and fire. For this reason, 9% Ni is typically used, since a ship requires high quality products with special materials and structural technologies that guarantee operability at cryogenic temperatures. However, there is an urgent need for research to derive a uniform welding quality, since high process difficulty and differences in welding quality related to a welder’s skills can cause a deterioration of the weld quality in the 9% Ni steel welding process. For 9% Ni steel, the higher the dilution ratio of the base metal, the lower the strength. In order to secure the required strength, excessive dilution of the base metal should be avoided, and the relationship between dilution ratio and strength should be investigated. According to previous research, if it exceeds 25% it may be lower than the API standard of 363 MPa for hardening welds. Therefore, in this study, the flux cored arc welding process is performed by establishing criteria that can be evaluated based on the SVM method in order to determine the structure of the weld to be cured according to the dilution rate of the base metal. We would like to propose a multipurpose optimization algorithm to ensure uniform quality of 9% Ni steel. Full article

(This article belongs to the Special Issue Welding Metallurgy)

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13 pages, 3589 KiB

Open AccessArticle

Experimental and Numerical Studies on Preparation of Thin AZ31B/AA5052 Composite Plates Using Improved Explosive Welding Technique

by Qi Wang, Xuejiao Li, Biming Shi and Yong Wu

Metals 2020, 10(8), 1023; https://doi.org/10.3390/met10081023 - 30 Jul 2020

Cited by 16 | Viewed by 2451

Abstract

In this work, an improved explosive welding technique was investigated to fabricate a thin Mg/Al plate, where an additional thin aluminum sheet was used as a buffer layer between the explosive and the Al plate, and the Mg plate was rigidly constrained by a steel plate to avoid excessive deformation. Moreover, the welding parameters were optimized using theoretical analysis and numerical simulation, and the interfacial behavior was simulated using the SPH method. The bonding properties of the achieved joints were investigated using microstructure observation and mechanical tests. It was concluded that this technique is an effective method for producing a thin Mg/Al composite plate. In both morphology observation and mechanical tests, an excellent bonding quality was confirmed. In addition, smoothed particle hydrodynamics (SPH) simulation revealed an extreme condition of local high temperature and plastic strain in the welding process, and the characteristic parameters of waves obtained using simulation are well congruous with the experiment. Full article

(This article belongs to the Special Issue Welding Metallurgy)

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12 pages, 4876 KiB

Open AccessArticle

Comparative Study of Droplet Transfer Modes on Appearance, Microstructure, and Mechanical Properties of Weld during Pulsed GMAW

by Peizhuo Zhai, Songbai Xue, Jianhao Wang, Yu Tao, Weizhong Chen, Tao Chen and Shilei Ji

Metals 2020, 10(5), 611; https://doi.org/10.3390/met10050611 - 8 May 2020

Cited by 13 | Viewed by 3168

Abstract

Droplet transfer plays a crucial role in welding stability and quality of pulsed gas metal arc weld (GMAW), referring to the process of heat and mass transition. In this work, the appearance, microstructure, microhardness, tensile properties, and impact toughness with three typical modes of droplet transfer in pulsed GMAW (ODMP: one drop per multiple pulses; ODPP: one drop per pulse; MDPP: multiple drops per pulse) were studied and compared. The results showed that the better welding appearance, the deeper penetration, and the less fume covered on the steel plate could be found during the ODPP welding process. At the same wire feeding speed and arc length, the average current was similar in ODPP and MDPP conditions. However, the average current in the ODMP condition was about 15 A larger than the other two, contributing to the higher heat input. Compared with MDPP and ODMP, the longest elongation and impact energy of the welded joint were found in the ODPP condition. Furthermore, the decrease of elongation and impact toughness in the ODMP condition might result from the higher heat input and the coarsen microstructure, like the proeutectoid ferrite and ferrite side plate. Full article

(This article belongs to the Special Issue Welding Metallurgy)

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Review

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40 pages, 11003 KiB

Open AccessEditor’s ChoiceReview

A Review on Laser-Assisted Joining of Aluminium Alloys to Other Metals

by Ivan Bunaziv, Odd M. Akselsen, Xiaobo Ren, Bård Nyhus, Magnus Eriksson and Sverre Gulbrandsen-Dahl

Metals 2021, 11(11), 1680; https://doi.org/10.3390/met11111680 - 21 Oct 2021

Cited by 17 | Viewed by 4139

Abstract

Modern industry requires different advanced metallic alloys with specific properties since conventional steels cannot cover all requirements. Aluminium alloys are becoming more popular, due to their low weight, high corrosion resistance, and relatively high strength. They possess respectable electrical conductivity, and their application extends to the energy sector. There is a high demand in joining aluminium alloys with other metals, such as steels, copper, and titanium. The joining of two or more metals is challenging, due to formation of the intermetallic compound (IMC) layer with excessive brittleness. High differences in the thermophysical properties cause distortions, cracking, improper dilution, and numerous weld imperfections, having an adverse effect on strength. Laser beam as a high concentration energy source is an alternative welding method for highly conductive metals, with significant improvement in productivity, compared to conventional joining processes. It may provide lower heat input and reduce the thickness of the IMC layer. The laser beam can be combined with arc-forming hybrid processes for wider control over thermal cycle. Apart from the IMC layer thickness, there are many other factors that have a strong effect on the weld integrity; their optimisation and innovation is a key to successfully delivering high-quality joints. Full article

(This article belongs to the Special Issue Welding Metallurgy)

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