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A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: closed (15 September 2022) | Viewed by 33023

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Prof. Dr. Shanping Lu

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Guest Editor

Institute of Metal Research, Chinese Academy of Sciences, 110016 Shenyang, China
Interests: welding material; welding metallurgy; welding technology; welding mechanics

Special Issue Information

Dear Colleagues,

The welding and joining technologies of materials remain the key technology used in the contemporary manufacture of industrial products for use in the engineering of automobiles, aircraft, ships, pressure vessels, pipelines, construction, bridges, and electronic equipment, and so on. In industry, various welding and joining processes such as arc welding, high energy beam welding, and friction stir welding have been developed. According to the structural requirements determined by the material characteristics, welding joint performance, and other factors, the most appropriate welding process is selected for manufacturing. In order to improve the efficiency and quality of welding processes, research is actively being carried out across the world to clarify the mechanisms of welding processes scientifically, and to develop more advanced welding processes. However, further work is needed in this field.

The Special Issue aims to present state-of-the-art scientific developments in welding technology, which include welding materials, welding metallurgy, material weldability, and the evaluation of welding joints. The topics of interest include, but are not limited to, the following:

Physical mechanisms of various advanced welding processes;
Weldability of metal materials in high-end equipment manufacturing engineering;
Welding metallurgy theory and the application of advanced metal materials;
Development and application of special welding materials.

Prof. Dr. Shanping Lu
Guest Editor

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Keywords

Special welding material
Welding metallurgy
Weldability
Experimental observation
Modeling and simulation
Process mechanism

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Published Papers (10 papers)

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Research

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12 pages, 9203 KiB

Open AccessArticle

Board Level Drop Test for Evaluating the Reliability of High-Strength Sn–Bi Composite Solder Pastes with Thermosetting Epoxy

by Lu Liu, Songbai Xue, Ruiyang Ni and Peng Zhang

Crystals 2022, 12(7), 924; https://doi.org/10.3390/cryst12070924 - 29 Jun 2022

Cited by 2 | Viewed by 3727

Abstract

The Sn–Bi solder paste is commonly used in electronic assembly and packaging, but its brittleness causes poor reliability in shock environments. In this study, the mechanical reliability of Sn–Bi solder paste and Sn–Bi composite solder paste with thermosetting epoxy (TSEP Sn–Bi) was investigated with the board level drop test. The crack characterizations of solder joints were evaluated using a stereomicroscope after the dye and pull test. The microstructure characterization and failure types of solder joints were analyzed by a scanning electron microscope (SEM), and an energy dispersive spectrometer (EDS) was employed to investigate the initial phase identification and elemental analysis. Compared with Sn–Bi solder paste, the results show that the TSEP Sn–Bi solder pastes reduced the proportion of the complete failure and partial failure of the solder joints during the drop test. The microstructure observation of the crack path showed that the Sn–Bi/TSEP Sn–Bi solder joints were reinforced through the cured epoxy resin. The number of drops of the Sn–Bi/TSEP Sn–Bi-x (x = 3, 5, 7) solder joints had 1.55, 2.57, and over 3.00 times that of Sn–Bi/Sn–Bi solder joints after the board level drop test. Full article

(This article belongs to the Special Issue Advances of Welding Materials)

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17 pages, 12247 KiB

Open AccessArticle

Study on Novel Powder Metallurgy Al-Si Brazing Filler Metal with Flux

by Wenpan Fei, Bo Wang, Yinbin Lou, Weimin Long, Jianfeng Deng, Lei Zhang, Pengzhi Yin and Shuiqing Wang

Crystals 2022, 12(4), 544; https://doi.org/10.3390/cryst12040544 - 13 Apr 2022

Cited by 2 | Viewed by 2917

Abstract

Green brazing is one of the key basic technologies in the manufacturing industry, and the wide application of composite brazing filler metals is a significant method for realizing green and automatic brazing. In the present study, an investigation was conducted into a novel powder metallurgy Al-Si brazing filler metal with flux and the resulting brazed joints of 3003/6061 aluminum alloy. By means of scanning electron microscopy and energy-dispersive analysis, the effect of moisture-resistance performance on the microstructure and the properties of Al-Si brazing filler metal with flux and brazing joint were analyzed. The results reveal that the new type of powder metallurgy Al-12Si brazing filler metal had better moisture-resistance performance than the seamed flux cored brazing filler metal. In an environment with a humidity of 90% and a temperature of 40 °C for 7 days, the moisture absorption rate of the powder metallurgy Al-12Si brazing filler metal with flux was only 0.17%. The wet spreading area of the new powder metallurgy Al-12Si brazing filler metal treated for 3 days in a humid environment was 320 mm², which was 7% less than that in the dry state. At the same time, the spreading area of the seamed flux cored brazing filler metal under the same conditions was only 80.9% of that in the dry state. The fracture strengths of the 3003 and 6061 aluminum alloy joints brazed by the wetted powder metallurgy Al-12Si brazing filler metal with flux were satisfactory, and scanning electron microscopy examination of the braze-zone revealed that relatively sound joints were obtained. However, obvious pores were observed in the braze-zone of the wetted seamed flux cored brazing filler. The maximum diameter of the pores was increased from 28 μm to 68 μm in the brazing area. Full article

(This article belongs to the Special Issue Advances of Welding Materials)

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15 pages, 8270 KiB

Open AccessArticle

Microstructure and Fatigue Properties of Resistance Element Welded Joints of DP500 Steel and AW 5754 H22 Aluminum Alloy

by Aleksija Đurić, Dragan Milčić, Zijah Burzić, Damjan Klobčar, Miodrag Milčić, Biljana Marković and Vladislav Krstić

Crystals 2022, 12(2), 258; https://doi.org/10.3390/cryst12020258 - 14 Feb 2022

Cited by 9 | Viewed by 3629

Abstract

The modern concept of lightweight design (LW) requires the application of different materials in one structure (multi-material structures). The structure of different materials has a good perspective for application in the automotive and aerospace industries but only if it is possible to achieve a quality joint between different materials. The most used technology for joining different materials in the automotive industry is Resistance spot welding (RSW). Due to different mechanical, physical, and chemical properties, the joining of different materials by RSW technology does not provide a quality joint, and accordingly, alternative technologies for joining different materials have emerged. Resistance element welding (REW) was developed to enable joint of different materials. This paper presents the welding of AW 5754 H22 Al alloy (1.0 mm-thick) and DP500 steel (1.5 mm-thick) using novel REW. The peak load, absorption energy, microstructure, microhardness and fatigue strength of the REW joint has been investigated. The joint of the same materials has been done also using conventional RSW to compare some results. The results that will be presented in this paper show that that REW can achieve reliable joining of the two materials at relatively low welding currents compared to RSW. Using REW process with a significantly lower welding current, satisfactory mechanical characteristics of the weld joint can be achieved, so peak load is between 2300–2500 N, displacement is between 2.5–3 mm and the absorption energy is between 3.3–5.7 J. REW joints showed fatigue strength with the fatigue limit of 882 N. Full article

(This article belongs to the Special Issue Advances of Welding Materials)

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12 pages, 6066 KiB

Open AccessArticle

Effect of In and Pr on the Microstructure and Properties of Low-Silver Filler Metal

by Jie Wu, Songbai Xue and Peng Zhang

Crystals 2021, 11(8), 929; https://doi.org/10.3390/cryst11080929 - 11 Aug 2021

Cited by 4 | Viewed by 1889

Abstract

The novel low-silver 12AgCuZnSn filler metals containing In and Pr were used for flame brazing of copper and 304 stainless steel in this study. The effects of In and Pr content on the melting temperature, wettability, mechanical properties and microstructure of 12AgCuZnSn filler metal were analyzed. The results indicate that the solidus and liquidus temperatures of filler metals decrease with the addition of In. Trace amounts of Pr have little impact on the melting temperature of the low-silver filler metals. In addition, the spreading area of filler metals on copper and 304 stainless steel is improved. The highest shear strength of brazed joint is 427 MPa when the content of In and Pr are 2 wt.% and 0.15 wt.%, respectively. Moreover, it is observed that the trace amount of Pr significantly refines the microstructure of brazed joint matrix. A bright Pr₃Cu₄Sn₄ phase is found in filler metal and brazing seam when the contents of In and Pr are 5 wt.% and 0.5 wt.%, respectively. Full article

(This article belongs to the Special Issue Advances of Welding Materials)

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10 pages, 3675 KiB

Open AccessArticle

Study on the Reliability of Sn–Bi Composite Solder Pastes with Thermosetting Epoxy under Thermal Cycling and Humidity Treatment

by Lu Liu, Songbai Xue, Ruiyang Ni, Peng Zhang and Jie Wu

Crystals 2021, 11(7), 733; https://doi.org/10.3390/cryst11070733 - 24 Jun 2021

Cited by 8 | Viewed by 3773

Abstract

In this study, a Sn–Bi composite solder paste with thermosetting epoxy (TSEP Sn–Bi) was prepared by mixing Sn–Bi solder powder, flux, and epoxy system. The melting characteristics of the Sn–Bi solder alloy and the curing reaction of the epoxy system were measured by differential scanning calorimeter (DSC). A reflow profile was optimized based on the Sn–Bi reflow profile, and the Organic Solderability Preservative (OSP) Cu pad mounted 0603 chip resistor was chosen to reflow soldering and to prepare samples of the corresponding joint. The high temperature and humidity reliability of the solder joints at 85 °C/85% RH (Relative Humidity) for 1000 h and the thermal cycle reliability of the solder joints from −40 °C to 125 °C for 1000 cycles were investigated. Compared to the Sn–Bi solder joint, the TSEP Sn–Bi solder joints had increased reliability. The microstructure observation shows that the epoxy resin curing process did not affect the transformation of the microstructure. The shear force of the TSEP Sn–Bi solder joints after 1000 cycles of thermal cycling test was 1.23–1.35 times higher than the Sn–Bi solder joint and after 1000 h of temperature and humidity tests was 1.14–1.27 times higher than the Sn–Bi solder joint. The fracture analysis indicated that the cured cover layer could still have a mechanical reinforcement to the TSEP Sn–Bi solder joints after these reliability tests. Full article

(This article belongs to the Special Issue Advances of Welding Materials)

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16 pages, 12124 KiB

Open AccessArticle

The Effect of Nickel Contents on the Microstructure Evolution and Toughness of 800 MPa Grade Low Carbon Bainite Deposited Metal

by Jingwu Liu, Jian Sun, Shitong Wei and Shanping Lu

Crystals 2021, 11(6), 709; https://doi.org/10.3390/cryst11060709 - 21 Jun 2021

Cited by 13 | Viewed by 2504

Abstract

In this work, three deposited metals with different nickel (Ni) contents were produced by active gas metal arc welding (GMAW) in order to explore the influence of Ni on the microstructure evolution and toughness of 800 MPa grade low carbon bainite deposited metal. The results showed that microstructure of the deposited metals mainly consisted of lath bainite, lath martensite, coalesced bainite (CB), and retained austenite (RA), and that the toughness was closely related to two factors: CB and RA. RA in deposited metal could improve the toughness, while the CB would deteriorate the toughness of deposited metal. As the Ni content increased, a large amount of CB was generated in the deposited metals. The RA content increased from 1.5% to 5.7% with the content of Ni increasing from 5.5% to 6.5%. However, the RA content did not increase when the Ni content increased from 6.5% to 7.5%. Additionally, the smallest control unit of toughness in 800 MPa grade low carbon bainite deposited metals is the Bain Packet (BP) from the perspective of crystallography characteristics. This work provided a reference for the chemical composition design of 800 MPa grade steel welding consumables and showed that the toughness of the deposited metal could be improved effectively by increasing the RA content while suppressing the formation of CB. Full article

(This article belongs to the Special Issue Advances of Welding Materials)

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10 pages, 42473 KiB

Open AccessArticle

Effects of Trace Oxygen Content on Microstructure and Performances of Au-20Sn/Cu Solder Joints

by Yang Li, Di Wu, Yabin Zhang, Liujue Wang and Songbai Xue

Crystals 2021, 11(6), 601; https://doi.org/10.3390/cryst11060601 - 26 May 2021

Cited by 1 | Viewed by 2355

Abstract

The Au-20Sn solder is widely used in the packaging of high-end electronic products, and the requirement on the reliability of the solder joints is more and more strict with a continuous increase in the performance of the package products. As the oxygen content in the Au-Sn solder is a key factor dominating the quality of fluxless packaging, in this study, the wettability and spreading performance of the Au-20Sn solder with different oxygen contents and the interfacial microstructure, mechanical properties, gas tightness and ratio of soldering area of the Au-Sn/Cu solder joints prepared using these solders were comprehensively investigated to clarify the effects of trace oxygen content. The results reveal that the wetting and spreading performances of the solder decrease sharply with increasing oxygen conte[nt. When the oxygen content increased from 18 to 77 ppm, the spreading area of the solder on the Cu substrate decreased from 92.8 to 49.2 mm², reducing by 47%. Meanwhile, pores and microcracks appear in the solder joint with relatively high oxygen content, making the shear strength decrease from 56.6 to 31.7 MPa. The oxygen also greatly affects the gas tightness and ratio of soldering area. For the optical window packaged using Au-Sn solder containing 40 ppm of oxygen, the leakage rate was higher than 5 × 10⁻¹¹ mbar·m⁻³·s⁻¹ and cannot fulfill the requirements. With increasing oxygen content in the Au-Sn solder, the cleanliness of the chip packaged with these solders deteriorated, and the solder surface was obviously oxidized. When the oxygen content was 18 ppm, the ratio of soldering area was 92%, but decreased sharply to 53% when the oxygen content increased to 77 ppm. It is demonstrated that an oxygen content lower than 27 ppm is required for the Au-20Sn solder used in fluxless packaging. Full article

(This article belongs to the Special Issue Advances of Welding Materials)

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12 pages, 48094 KiB

Open AccessArticle

Study on Microstructure and Properties of 12Ag–Cu–Zn–Sn Cadmium-Free Filler Metals with Trace In Addition

by Jie Wu, Songbai Xue, Zhen Yao and Weimin Long

Crystals 2021, 11(5), 557; https://doi.org/10.3390/cryst11050557 - 16 May 2021

Cited by 10 | Viewed by 2560

Abstract

The effect of different In contents on the melting characteristics, mechanical properties, and microstructure of 12Ag–Cu–Zn–Sn filler metal was investigated in this paper, and flame brazing of 304 stainless steel and copper plates was done using the 12Ag–Cu–Zn–Sn–xIn filler metal. The results indicate that adding appropriate amount of In can evidently decrease the solidus and liquidus temperatures and improve the wettability of the low silver based filler metals. In addition, the shear strength of 304 stainless steel and copper plates joint brazed by 12Ag–Cu–Zn–Sn–1In are satisfactory due to the solution strength effect, and scanning electron microscopy examination of the braze-zone revealed that more relatively sound joints were obtained when brazing was done with 12Ag–Cu–Zn–Sn–xIn filler metal than with Indium free one; its performance is comparable to that of the joint brazed with the 20Ag–Cu–Zn–Sn filler metal, having a remarkable silver-saving effect. Full article

(This article belongs to the Special Issue Advances of Welding Materials)

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Review

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19 pages, 10419 KiB

Open AccessReview

Influences of Sn on Properties of Ag-Based and Cu-Based Brazing Filler Metals

by Qingcheng Luo, Songbai Xue and Jie Wu

Crystals 2021, 11(11), 1403; https://doi.org/10.3390/cryst11111403 - 18 Nov 2021

Cited by 16 | Viewed by 3465

Abstract

Ag-based and Cu-based brazing filler metals, which are the most widely used brazing materials in industrial manufacturing, have excellent gap-filling properties and can braze almost all the metallic materials and their alloys, except for the low-melting-point metals such as Al and Mg. Therefore, Ag-based and Cu-based brazing filler metals have attracted great attention. In this review, three series of typical Ag-based filler metals: the Ag-Cu, Ag-Cu-Zn, and Ag-Cu-Zn-Sn alloys; and three series of Cu-based filler metals: the crystalline and amorphous Cu-P filler metals, as well as the Cu-Zn filler metals, were chosen as the representatives. The latest research progress on Sn-containing Ag-based and Cu-based brazing filler metals is summarized, and the influences of Sn on the melting characteristics, wettability, microstructure, and mechanical properties of the selected filler metals are analyzed. Based on these, the problems and corresponding solutions in the investigation and application of the Sn-containing Ag-based and Cu-based filler metals are put forward, and the research and development trends of these filler metals are proposed. Full article

(This article belongs to the Special Issue Advances of Welding Materials)

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17 pages, 5141 KiB

Open AccessReview

Research Progress in Relation to Composite Brazing Materials with Flux

by Bo Wang, Weimin Long, Mengfan Wang, Pengzhi Yin, Shaokang Guan, Sujuan Zhong and Songbai Xue

Crystals 2021, 11(9), 1045; https://doi.org/10.3390/cryst11091045 - 30 Aug 2021

Cited by 7 | Viewed by 4782

Abstract

Brazing was one of the earliest material-joining methods to be invented and widely used by humans. In the past 30 years, the technology and materials employed for brazing have developed rapidly and continuously. With the rise of the international new industrial revolution, the manufacturing industry is moving towards diversification, and brazing filler metals are also evolving in the direction of eco-friendliness, compounding and diversification. In the “carbon neutral” environment of 2021, green composite brazing materials will become mainstream. In this paper, the classification and characteristics of flux-containing brazing materials are summarized, and the preparation technology, composition design and typical application of composite brazing materials such as flux-cored brazing filler metal, flux-coated brazing filler metal and powder metallurgy brazing filler metal are analyzed. The article highlights the problems encountered in the research and development of composite brazing materials and proposes future development directions, such as with low-silver and cadmium-free brazing filler metals, the creation of new powder brazing filler metal-forming technology and improvements to the quality of brazing filler metals by shape control and performance optimization, to accelerate the process of brazing automation. Full article

(This article belongs to the Special Issue Advances of Welding Materials)

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