Special Issue "Advances in Welding Metal Alloys, Dissimilar Metals and Additively Manufactured Parts"

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (31 August 2016)

Special Issue Editor

Guest Editor
Prof. Dr. Giuseppe Casalino

Dip. di Meccanica, Matematica e Management, Politecnico di Bari, Viale Japigia 182, 70126 Bari, Italy
Website1 | Website2 | E-Mail
Interests: welding; laser materials processing; numerical and analytical modeling of manufacturing processes

Special Issue Information

Dear Colleagues,

Welding is a material-joining process, commonly associated with metals, in which two or more parts are coalesced at their contacting surfaces by a suitable application of heat and/or pressure. Welding techniques are innovative, well established, and their combinations are available to join materials with a number of geometries, which provide an opportunity to solve many engineering problems.

Metals is dedicating a Special Issue on the following aspects of welding technologies: modeling and simulation; evolution of microstructure and properties in welds; prediction of residual stress, distortion, fatigue, and corrosion; weld quality and qualification; and destructive and non-destructive control.

Papers on laser welding, friction stir welding, electron beam welding, arc welding, and hybrid welding are welcome. In particular, the journal will be pleased to publish research on light metal alloys, dissimilar metals, and additively manufactured parts.

Contributions from around the world will contribute to the success of this Special Issue, which aims at spreading the potential of advanced welding at joining well-established and innovative metallic parts.

Dr. Giuseppe Casalino
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Metals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • advanced welding
  • metal alloys
  • dissimilar weld
  • additively manufactured parts
  • evolution of microstructure
  • properties in welds

Published Papers (18 papers)

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Editorial

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Open AccessEditorial Advances in Welding Metal Alloys, Dissimilar Metals and Additively Manufactured Parts
Metals 2017, 7(2), 32; doi:10.3390/met7020032
Received: 10 January 2017 / Revised: 23 January 2017 / Accepted: 23 January 2017 / Published: 25 January 2017
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Abstract
Nowadays, strong, light-weight, multi-functional, high performing products are key for achieving success in the worldwide markets. Meeting those requirements calls for enabling technologies that lead to innovative and sustainable manufacturing [1].[...] Full article

Research

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Open AccessFeature PaperArticle An Investigation of the Mechanical Properties of a Weldment of 7% Nickel Alloy Steels
Metals 2016, 6(11), 285; doi:10.3390/met6110285
Received: 31 August 2016 / Revised: 14 November 2016 / Accepted: 14 November 2016 / Published: 19 November 2016
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Abstract
During the last decade, the demand for natural gas has steadily increased for the prevention of environmental pollution. For this reason, many liquefied natural gas (LNG) carriers have been manufactured. Since one of the most important issues in the design of LNG carriers
[...] Read more.
During the last decade, the demand for natural gas has steadily increased for the prevention of environmental pollution. For this reason, many liquefied natural gas (LNG) carriers have been manufactured. Since one of the most important issues in the design of LNG carriers is to guarantee structural safety, the use of low-temperature materials is increasing. Among commonly employed low-temperature materials, nickel steel has many benefits such as good strength and outstanding corrosion resistance. Accordingly, nickel steels are one of the most commonly used low-temperature steels for LNG storage tanks. However, the study of fracture toughness with various welding consumables of 7% nickel alloy steel is insufficient for ensuring the structural safety of LNG storage tanks. Therefore, the aim of this study was to evaluate fracture toughness of several different weldments for 7% nickel alloy steels. The weldment of 7% nickel alloy steel was fabricated by tungsten inert gas (TIG), flux cored arc welding (FCAW), and gas metal arc welding (GMAW). In order to assess the material performance of the weldments at low temperature, fracture toughness such as crack tip opening displacement (CTOD) and the absorbed impact energy of weldments were compared with those of 9% nickel steel weldments. Full article
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Open AccessArticle An Analysis of the Weldability of Ductile Cast Iron Using Inconel 625 for the Root Weld and Electrodes Coated in 97.6% Nickel for the Filler Welds
Metals 2016, 6(11), 283; doi:10.3390/met6110283
Received: 26 July 2016 / Revised: 5 November 2016 / Accepted: 14 November 2016 / Published: 18 November 2016
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Abstract
This article examines the weldability of ductile cast iron when the root weld is applied with a tungsten inert gas (TIG) welding process employing an Inconel 625 source rod, and when the filler welds are applied with electrodes coated with 97.6% Ni. The
[...] Read more.
This article examines the weldability of ductile cast iron when the root weld is applied with a tungsten inert gas (TIG) welding process employing an Inconel 625 source rod, and when the filler welds are applied with electrodes coated with 97.6% Ni. The welds were performed on ductile cast iron specimen test plates sized 300 mm × 90 mm × 10 mm with edges tapered at angles of 60°. The plates were subjected to two heat treatments. This article analyzes the influence on weldability of the various types of electrodes and the effect of preheat treatments. Finally, a microstructure analysis is made of the material next to the weld in the metal-weld interface and in the weld itself. The microstructure produced is correlated with the strength of the welds. We treat an alloy with 97.6% Ni, which prevents the formation of carbides. With a heat treatment at 900 °C and 97.6% Ni, there is a dissolution of all carbides, forming nodules in ferritic matrix graphite. Full article
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Open AccessFeature PaperArticle Tool Wear Characteristics and Effect on Microstructure in Ti-6Al-4V Friction Stir Welded Joints
Metals 2016, 6(11), 275; doi:10.3390/met6110275
Received: 24 September 2016 / Revised: 3 November 2016 / Accepted: 4 November 2016 / Published: 10 November 2016
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Abstract
In the present paper, tool wear and the rate of wear during friction stir welding (FSW) of Ti-6Al-4V alloy are investigated. A conical tungsten carbide tool was used to produce butt-type friction stir welded joints in two-millimeter thick Ti-6Al-4V sheets. An original design
[...] Read more.
In the present paper, tool wear and the rate of wear during friction stir welding (FSW) of Ti-6Al-4V alloy are investigated. A conical tungsten carbide tool was used to produce butt-type friction stir welded joints in two-millimeter thick Ti-6Al-4V sheets. An original design of a movable pin allowed for the examination of the tool damage for each process condition. The influence of tool degradation on the quality of the welded joints and the damage brought to the microstructure are examined and discussed. For this purpose, optical and scanning electron microscopies as well as EDX analyses were used to examine the tool wear and the resulting macrostructures and microstructures. The type and nature of the defects are also analyzed as a function of FSW processing parameters. Important geometry and weight variations were observed on the pin and shoulder for all welding conditions, in particular when low tool rotation and travel speeds were used. Experimental results also show that the radial wear of the pin is not uniform, indicating the presence of important frictional temperature gradients through the thickness of the joint. The maximum wear was measured at a location of about one millimeter from the pin root center. Finally, tool rotation was determined as the most significant process parameter influencing both tool wear and microstructure of the joints. Full article
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Open AccessArticle Weldability and Monitoring of Resistance Spot Welding of Q&P and TRIP Steels
Metals 2016, 6(11), 270; doi:10.3390/met6110270
Received: 12 October 2016 / Revised: 4 November 2016 / Accepted: 4 November 2016 / Published: 8 November 2016
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Abstract
This work aims at investigating the spot weldability of a new advanced Quenching and Partitioning (Q&P) steel and a Transformation Induced Plasticity (TRIP) steel for automotive applications by evaluating the effects of the main welding parameters on the mechanical performance of their dissimilar
[...] Read more.
This work aims at investigating the spot weldability of a new advanced Quenching and Partitioning (Q&P) steel and a Transformation Induced Plasticity (TRIP) steel for automotive applications by evaluating the effects of the main welding parameters on the mechanical performance of their dissimilar spot welds. The welding current, the electrode tip voltage and the electrical resistance of sheet stack were monitored in order to detect any metal expulsion and to evaluate its severity, as well as to clarify its effect on spot strength. The joint strength was assessed by means of shear and cross tension tests. The corresponding fracture modes were determined through optical microscopy. The welding current is the main process parameter that affects the weld strength, followed by the clamping force and welding time. Metal expulsion can occur through a single large expulsion or multiple expulsions, whose effects on the shear and cross tension strength have been assessed. Longer welding times can limit the negative effect of an expulsion if it occurs in the first part of the joining process. The spot welds exhibit different fracture modes according to their strengths. Overall, a proper weldability window for the selected process parameters has been determined to obtain sound joints. Full article
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Open AccessArticle The Interfacial Microstructure and Mechanical Properties of Diffusion-Bonded Joints of 316L Stainless Steel and the 4J29 Kovar Alloy Using Nickel as an Interlayer
Metals 2016, 6(11), 263; doi:10.3390/met6110263
Received: 28 August 2016 / Revised: 19 October 2016 / Accepted: 19 October 2016 / Published: 3 November 2016
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Abstract
316L stainless steel (Fe–18Cr–11Ni) and a Kovar (Fe–29Ni–17Co or 4J29) alloy were diffusion-bonded via vacuum hot-pressing in a temperature range of 850–950 °C with an interval of 50 °C for 120 min and at 900 °C for 180 and 240 min, under a
[...] Read more.
316L stainless steel (Fe–18Cr–11Ni) and a Kovar (Fe–29Ni–17Co or 4J29) alloy were diffusion-bonded via vacuum hot-pressing in a temperature range of 850–950 °C with an interval of 50 °C for 120 min and at 900 °C for 180 and 240 min, under a pressure of 34.66 MPa. Interfacial microstructures of diffusion-bonded joints were characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). The inter-diffusion of the elements across the diffusion interface was revealed via electron probe microanalysis (EPMA). The mechanical properties of the joints were investigated via micro Vickers hardness and tensile strength. The results show that an Ni interlayer can serve as an effective diffusion barrier for the bonding of 316L stainless steel and the 4J29 Kovar alloy. The composition of the joints was 316L/Ni s.s (Fe–Cr–Ni)/remnant Ni/Ni s.s (Fe–Co–Ni)/4J29. The highest tensile strength of 504.91 MPa with an elongation of 38.75% was obtained at 900 °C for 240 min. After the width of nickel solid solution (Fe–Co–Ni) sufficiently increased, failure located at the 4J29 side and the fracture surface indicated a ductile nature. Full article
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Open AccessFeature PaperArticle Microstructure and Mechanical Properties of Friction Stir Welded Dissimilar Titanium Alloys: TIMET-54M and ATI-425
Metals 2016, 6(10), 252; doi:10.3390/met6100252
Received: 14 September 2016 / Revised: 10 October 2016 / Accepted: 17 October 2016 / Published: 24 October 2016
Cited by 1 | PDF Full-text (4866 KB) | HTML Full-text | XML Full-text
Abstract
Weight reduction in automobiles and in aerospace industries can profoundly register for the behemoth change in the consumption of the fossil fuels and, in turn, CO2 emission. With a promising hope in hindsight for weight reduction, we have successfully produced butt joints
[...] Read more.
Weight reduction in automobiles and in aerospace industries can profoundly register for the behemoth change in the consumption of the fossil fuels and, in turn, CO2 emission. With a promising hope in hindsight for weight reduction, we have successfully produced butt joints of friction stir welded (FSWed) dissimilar, and rather novice, α-β titanium alloys—ATI-425 and TIMET-54M. The study presented in this article encompasses the microstructural and mechanical properties of the joints for two cases, (1) ATI-425 on the advancing side; and (2) TIMET-54M on the advancing side. The evolution of microstructure and concomitant mechanical properties are characterized by optical microscopy, microhardness, and tensile properties. A detailed description of the microstructural evolution and its correlation with the mechanical properties have been presented in this study. Our investigations suggest that mixing patterns are dependent on the location (advancing, or retreating) of the alloying sheet. However, the microstructure in the weld nugget (WN) is quite similar (grain boundary α, and basket weave morphology consisting of α + β lamellae) in both cases with traces of untransformed β. The thermo-mechanically affected zone (TMAZ) on the either side of the weld is primarily affected by the microstructure of the base material (BM). A noticeable increase in the hardness values in the WN is accompanied by significant deflection on the advancing and retreating sides. The tensile properties extracted from the global stress strain curves are comparable with minimal difference for both cases. In both cases, the fracture occurred on the retreating side of the weld. Full article
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Open AccessFeature PaperArticle Microstructure and Mechanical Properties of Dissimilar Friction Stir Welding between Ultrafine Grained 1050 and 6061-T6 Aluminum Alloys
Metals 2016, 6(10), 249; doi:10.3390/met6100249
Received: 25 August 2016 / Revised: 12 October 2016 / Accepted: 15 October 2016 / Published: 21 October 2016
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Abstract
The ultrafine grained (UFGed) 1050 Al plates with a thickness of 2 mm, which were produced by the accumulative roll bonding technique after five cycles, were friction stir butt welded to 2 mm thick 6061-T6 Al alloy plates at a different revolutionary pitch
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The ultrafine grained (UFGed) 1050 Al plates with a thickness of 2 mm, which were produced by the accumulative roll bonding technique after five cycles, were friction stir butt welded to 2 mm thick 6061-T6 Al alloy plates at a different revolutionary pitch that varied from 0.5 to 1.25 mm/rev. In the stir zone, the initial nano-sized lamellar structure of the UFGed 1050 Al alloy plate transformed into an equiaxial grain structure with a larger average grain size due to the dynamic recrystallization and subsequent grain growth. However, an equiaxial grain structure with a much smaller grain size was simultaneously formed in the 6061 Al alloy plates, together with coarsening of the precipitates. Tensile tests of the welds obtained at different welding speeds revealed that two kinds of fracture modes occurred for the specimens depending on their revolutionary pitches. The maximum tensile strength was about 110 MPa and the fractures were all located in the stir zone close to the 1050 Al side. Full article
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Open AccessArticle The Optimization of Process Parameters and Microstructural Characterization of Fiber Laser Welded Dissimilar HSLA and MART Steel Joints
Metals 2016, 6(10), 245; doi:10.3390/met6100245
Received: 22 July 2016 / Revised: 9 October 2016 / Accepted: 10 October 2016 / Published: 18 October 2016
Cited by 4 | PDF Full-text (6619 KB) | HTML Full-text | XML Full-text
Abstract
Nowadays, environmental impact, safety and fuel efficiency are fundamental issues for the automotive industry. These objectives are met by using a combination of different types of steels in the auto bodies. Therefore, it is important to have an understanding of how dissimilar materials
[...] Read more.
Nowadays, environmental impact, safety and fuel efficiency are fundamental issues for the automotive industry. These objectives are met by using a combination of different types of steels in the auto bodies. Therefore, it is important to have an understanding of how dissimilar materials behave when they are welded. This paper presents the process parameters’ optimization procedure of fiber laser welded dissimilar high strength low alloy (HSLA) and martensitic steel (MART) steel using a Taguchi approach. The influence of laser power, welding speed and focal position on the mechanical and microstructural properties of the joints was determined. The optimum parameters for the maximum tensile load-minimum heat input were predicted, and the individual significance of parameters on the response was evaluated by ANOVA results. The optimum levels of the process parameters were defined. Furthermore, microstructural examination and microhardness measurements of the selected welds were conducted. The samples of the dissimilar joints showed a remarkable microstructural change from nearly fully martensitic in the weld bead to the unchanged microstructure in the base metals. The heat affected zone (HAZ) region of joints was divided into five subzones. The fusion zone resulted in an important hardness increase, but the formation of a soft zone in the HAZ region. Full article
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Open AccessFeature PaperArticle TIG Dressing Effects on Weld Pores and Pore Cracking of Titanium Weldments
Metals 2016, 6(10), 243; doi:10.3390/met6100243
Received: 10 August 2016 / Revised: 30 September 2016 / Accepted: 10 October 2016 / Published: 17 October 2016
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Abstract
Weld pores redistribution, the effectiveness of using tungsten inert gas (TIG) dressing to remove weld pores, and changes in the mechanical properties due to the TIG dressing of Ti-3Al-2.5V weldments were studied. Moreover, weld cracks due to pores were investigated. The results show
[...] Read more.
Weld pores redistribution, the effectiveness of using tungsten inert gas (TIG) dressing to remove weld pores, and changes in the mechanical properties due to the TIG dressing of Ti-3Al-2.5V weldments were studied. Moreover, weld cracks due to pores were investigated. The results show that weld pores less than 300 μm in size are redistributed or removed via remelting due to TIG dressing. Regardless of the temperature condition, TIG dressing welding showed ductility, and there was a loss of 7% tensile strength of the weldments. Additionally, it was considered that porosity redistribution by TIG dressing was due to fluid flow during the remelting of the weld pool. Weld cracks in titanium weldment create branch cracks around pores that propagate via the intragranular fracture, and oxygen is dispersed around the pores. It is suggested that the pore locations around the LBZ (local brittle zone) and stress concentration due to the pores have significant effects on crack initiation and propagation. Full article
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Open AccessArticle An Assessment of the Mechanical Properties and Microstructural Analysis of Dissimilar Material Welded Joint between Alloy 617 and 12Cr Steel
Metals 2016, 6(10), 242; doi:10.3390/met6100242
Received: 29 August 2016 / Revised: 29 September 2016 / Accepted: 10 October 2016 / Published: 14 October 2016
Cited by 1 | PDF Full-text (4191 KB) | HTML Full-text | XML Full-text
Abstract
The most effective method to reduce CO2 gas emission from the steam power plant is to improve its performance by elevating the steam temperature to more than 700 °C. For this, it is necessary to develop applicable materials at high temperatures. Ni-based
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The most effective method to reduce CO2 gas emission from the steam power plant is to improve its performance by elevating the steam temperature to more than 700 °C. For this, it is necessary to develop applicable materials at high temperatures. Ni-based Alloy 617 and 12Cr steel are used in steam power plants, due to their remarkable mechanical properties, high corrosion resistance, and creep strength. However, since Alloy 617 and 12Cr steel have different chemical compositions and thermal and mechanical properties, it is necessary to develop dissimilar material welding technologies. Moreover, in order to guarantee the reliability of dissimilar material welded structures, the assessment of mechanical and metallurgical properties, fatigue strength, fracture mechanical analysis, and welding residual stress analysis should be conducted on dissimilar material welded joints. In this study, first, multi-pass dissimilar material welding between Alloy 617 and 12Cr steel was performed under optimum welding conditions. Next, mechanical properties were assessed, including the static tensile strength, hardness distribution, and microstructural analysis of a dissimilar material welded joint. The results indicated that the yield strength and tensile strength of the dissimilar metal welded joint were higher than those of the Alloy 617 base metal, and lower than those of the 12Cr steel base metal. The hardness distribution of the 12Cr steel side was higher than that of Alloy 617 and the dissimilar material weld metal zone. It was observed that the microstructure of Alloy 617 HAZ was irregular austenite grain, while that of 12Cr steel HAZ was collapsed martensite grain, due to repeatable heat input during multi-pass welding. Full article
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Open AccessArticle The Effects of Pulse Parameters on Weld Geometry and Microstructure of a Pulsed Laser Welding Ni-Base Alloy Thin Sheet with Filler Wire
Metals 2016, 6(10), 237; doi:10.3390/met6100237
Received: 31 August 2016 / Revised: 23 September 2016 / Accepted: 28 September 2016 / Published: 8 October 2016
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Abstract
Due to its excellent resistance to corrosive environments and its superior mechanical properties, the Ni-based Hastelloy C-276 alloy was chosen as the material of the stator and rotor cans of a nuclear main pump. In the present work, the Hastelloy C-276 thin sheet
[...] Read more.
Due to its excellent resistance to corrosive environments and its superior mechanical properties, the Ni-based Hastelloy C-276 alloy was chosen as the material of the stator and rotor cans of a nuclear main pump. In the present work, the Hastelloy C-276 thin sheet 0.5 mm in thickness was welded with filler wire by a pulsed laser. The results indicated that the weld pool geometry and microstructure were significantly affected by the duty ratio, which was determined by the pulse duration and repetition rate under a certain heat input. The fusion zone area was mainly affected by the duty ratio, and the relationship was given by a quadratic polynomial equation. The increase in the duty ratio coarsened the grain size, but did not obviously affect microhardness. The weld geometry and base metal dilution rate was manipulated by controlling pulsed parameters without causing significant change to the performance of the weld. However, it should be noted that, with a larger duty ratio, the partial molten zone is a potential weakness of the weld. Full article
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Open AccessArticle Influences of Laser Spot Welding on Magnetic Property of a Sintered NdFeB Magnet
Metals 2016, 6(9), 202; doi:10.3390/met6090202
Received: 11 May 2016 / Revised: 20 August 2016 / Accepted: 22 August 2016 / Published: 26 August 2016
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Abstract
Laser welding has been considered as a promising method to join sintered NdFeB permanent magnets thanks to its high precision and productivity. However, the influences of laser welding on the magnetic property of NdFeB are still not clear. In the present paper, the
[...] Read more.
Laser welding has been considered as a promising method to join sintered NdFeB permanent magnets thanks to its high precision and productivity. However, the influences of laser welding on the magnetic property of NdFeB are still not clear. In the present paper, the effects of laser power on the remanence (Br) were experimentally investigated in laser spot welding of a NdFeB magnet (N48H). Results show that the Br decreased with the increase of laser power. For the same welding parameters, the Br of magnets, that were magnetized before welding, were much lower than that of magnets that were magnetized after welding. The decrease in Br of magnets after laser welding resulted from the changes in microstructures and, in turn, the deterioration of magnetic properties in the nugget and the heat affected zone (HAZ) in a laser weld. It is recommended that the dimensions of nuggets and HAZ in laser welds of a NdFeB permanent magnet should be as small as possible, and the magnets should be welded before being magnetized in order to achieve a better magnetic performance in practical engineering applications. Full article
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Open AccessArticle The Effects of Laser Welding Direction on Joint Quality for Non-Uniform Part-to-Part Gaps
Metals 2016, 6(8), 184; doi:10.3390/met6080184
Received: 25 May 2016 / Revised: 2 August 2016 / Accepted: 3 August 2016 / Published: 6 August 2016
Cited by 2 | PDF Full-text (22008 KB) | HTML Full-text | XML Full-text
Abstract
Controlling part-to-part gaps is a crucial task in the laser welding of galvanized steel sheets for ensuring the quality of the assembly joint. However, part-to-part gaps are frequently non-uniform. Hence, elevations and depressions from the perspective of the heading direction of the laser
[...] Read more.
Controlling part-to-part gaps is a crucial task in the laser welding of galvanized steel sheets for ensuring the quality of the assembly joint. However, part-to-part gaps are frequently non-uniform. Hence, elevations and depressions from the perspective of the heading direction of the laser beam always exist throughout the gap, creating ascending, descending, and flat travelling paths for laser welding. In this study, assuming non-uniform part-to-part gaps, the effects of welding direction on the quality of the joint of galvanized steel sheets—SGARC440 (lower part) and SGAFC590DP (upper part)—were examined using 2-kW fiber and 6.6-kW disk laser welding systems. The experimental analysis of coupon tests confirmed that there is no statistically significant correlation between the direction of welding and weld pool quality if the gap exceeds the tolerable range. However, when the gap is controlled within the tolerable range, the welding direction can be considered as an important process control variable to enhance the quality of the joint. Full article
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Open AccessArticle Gas Metal Arc Welding Using Novel CaO-Added Mg Alloy Filler Wire
Metals 2016, 6(7), 155; doi:10.3390/met6070155
Received: 25 February 2016 / Revised: 18 June 2016 / Accepted: 23 June 2016 / Published: 8 July 2016
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Abstract
Novel “ECO Mg” alloys, i.e., CaO-added Mg alloys, which exhibit oxidation resistance during melting and casting processes, even without the use of beryllium or toxic protection gases such as SF6, have recently been introduced. Research on ECO Mg alloys is still
[...] Read more.
Novel “ECO Mg” alloys, i.e., CaO-added Mg alloys, which exhibit oxidation resistance during melting and casting processes, even without the use of beryllium or toxic protection gases such as SF6, have recently been introduced. Research on ECO Mg alloys is still continuing, and their application as welding filler metals was investigated in this study. Mechanical and metallurgical aspects of the weldments were analysed after welding, and welding behaviours such as fume generation and droplet transfer were observed during welding. The tensile strength of welds was slightly increased by adding CaO to the filler metal, which resulted from the decreased grain size in the weld metal. When welding Mg alloys, fumes have been unavoidable so far because of the low boiling temperature of Mg. Fume reduction was successfully demonstrated with a wire composed of the novel ECO Mg filler. In addition, stable droplet transfer was observed and spatter suppression could be expected by using CaO-added Mg filler wire. Full article
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Open AccessArticle Effects of Reflow Time on the Interfacial Microstructure and Shear Behavior of the SAC/FeNi-Cu Joint
Metals 2016, 6(5), 109; doi:10.3390/met6050109
Received: 21 March 2016 / Revised: 26 April 2016 / Accepted: 28 April 2016 / Published: 11 May 2016
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Abstract
Effects of reflow time on the interfacial microstructure and shear strength of the SAC/FeNi-Cu connections were investigated. It was found that the amount of Cu6Sn5 within the solder did not have a noticeable increase after a long time period of
[...] Read more.
Effects of reflow time on the interfacial microstructure and shear strength of the SAC/FeNi-Cu connections were investigated. It was found that the amount of Cu6Sn5 within the solder did not have a noticeable increase after a long time period of reflowing, indicating that the electro-deposited FeNi layer blocked the Cu atoms effectively into the solder area during a long period under liquid-conditions. The ball shear test results showed that the SAC/FeNi-Cu joint had a comparable strength to the SAC/Cu joint after reflowing, and the strength drop after reflowing for 210 s was less than that of the SAC/Cu joint. Full article
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Open AccessArticle Microstructure and Mechanical Properties of Friction Welding Joints with Dissimilar Titanium Alloys
Metals 2016, 6(5), 108; doi:10.3390/met6050108
Received: 5 April 2016 / Revised: 27 April 2016 / Accepted: 5 May 2016 / Published: 10 May 2016
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Abstract
Titanium alloys, which are important in aerospace application, offer different properties via changing alloys. As design complexity and service demands increase, dissimilar welding of the titanium alloys becomes a particular interest. Linear friction welding (LFW) is a relatively novel bond technique and has
[...] Read more.
Titanium alloys, which are important in aerospace application, offer different properties via changing alloys. As design complexity and service demands increase, dissimilar welding of the titanium alloys becomes a particular interest. Linear friction welding (LFW) is a relatively novel bond technique and has been successfully applied for joining titanium alloys. In this paper, dissimilar joints with Ti-6Al-4V and Ti-5Al-2Sn-2Zr-4Mo-4Cr alloys were produced by LFW process. Microstructure was studied via optical microscopy and scanning electron microscopy (SEM), while the chemical composition across the welded samples was identified by energy dispersive X-ray spectroscopy. Mechanical tests were performed on welded samples to study the joint mechanical properties and fracture characteristics. SEM was carried out on the fracture surface to reveal their fracture modes. A significant microstructural change with fine re-crystallization grains in the weld zone (WZ) and small recrystallized grains in the thermo-mechanically affected zone on the Ti-6Al-4V side was discovered in the dissimilar joint. A characteristic asymmetrical microhardness profile with a maximum in the WZ was observed. Tensile properties of the dissimilar joint were comparable to the base metals, but the impact toughness exhibited a lower value. Full article
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Open AccessArticle Low Cycle Fatigue Behaviors of Alloy 617 (INCONEL 617) Weldments for High Temperature Applications
Metals 2016, 6(5), 100; doi:10.3390/met6050100
Received: 15 March 2016 / Revised: 20 April 2016 / Accepted: 25 April 2016 / Published: 28 April 2016
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Abstract
In this study, we comparatively investigate the low cycle fatigue behavior of Alloy 617 (INCONEL 617) weldments by gas tungsten arc welding process at room temperature and 800 °C in the air to support the qualification in high temperature applications of the Next
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In this study, we comparatively investigate the low cycle fatigue behavior of Alloy 617 (INCONEL 617) weldments by gas tungsten arc welding process at room temperature and 800 °C in the air to support the qualification in high temperature applications of the Next Generation-IV Nuclear Plant. Axial total-strain controlled tests have been performed with the magnitude of strain ranges with a constant strain ratio (Rε = 1). The results of fatigue tests consistently show lower fatigue life with an increase in total strain range and temperature at all testing conditions. The reduction in fatigue life may result from the higher cyclic plastic strain accumulation and the material ductility at high temperature conditions. A constitutive behavior of high temperature by some cyclic hardening was observed. The occurrence of serrated yielding in the cyclic stress response was also observed, suggesting the influence of dynamic strain aging during high temperature. We evaluated a well-known life prediction model through the Coffin-Manson relationship. The results are well matched with the experimental data. In addition, low cycle fatigue cracking occurred in the weld metal region and initiated transgranularly at the free surface. Full article
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