Ultrasonic-Assisted Soldering of 5056 Aluminum Alloy Using Quasi-Melting Zn-Sn Alloy

To obtain sound butt-joints of 5056 aluminum alloy rods, ultrasonic-assisted soldering was conducted using Zn-18Sn and Zn-60Sn alloys. Each solder foil was inserted between rods of 5056 aluminum alloy. Ultrasonic vibration was propagated to faying surfaces at soldering temperatures below the liquidus temperature of the solder alloys, and then the samples were air cooled to room temperature. The optimum vibration time at the soldering temperature must be more than 2 seconds to have complete wetting and less than 4 seconds to avoid excessive dissolution of the 5056 alloy. The 5056 alloy joints soldered using quasi-melting. Zn-Sn alloys showed greater strength than the joints soldered at the temperatures over its respective liquidus temperature. As the soldering temperature was increased, the increased formation of the intermetallic compound Mg₂Sn or phases containing Mg generated by dissolution of 5056 into the solder layer decreased the joint strength. Ultrasonic-assisted soldering at an optimum temperature between solidus and liquidus of the Zn-Sn alloys is an important consideration for producing sound joints with sufficient strength.     

Effect of Aging Temperature on the Microstructure and Shear Strength of SAC0307-0.1Ni Lead-Free Solders in Copper Joints

This paper presents an investigation of the effects of aging temperature on the microstructure and shear strength of SAC0307-0.1Ni/Cu solder joints. Single-overlap shear solder joints were aged for 1 h at 80, 130, and 180°C. The microstructure of the interface between the solder and the Cu substrate contained phase of the intermetallic compounds (IMCs) (Cu,Ni)6Sn5 formed along the interface. The shape of scallop-like (Cu,Ni)6Sn5 IMCs changed to the long dendrite and grew larger at the interface of solder joints after increased aging temperature. In addition, a phase of particle-like Ag3Sn IMCs was formed in the solder matrix. The growth of the interfacial IMC layer in the solder joints increased with increasing the aging temperature. The thickness of this layer was controlled by diffusion mechanism. The shear strength of the as-reflowed solder joints was greater than that of the aged solder joints, and the shear strength of all the aged solder joints decreased with increasing the aging temperatures. Therefore, the aging temperature mainly affected the thickness of the interfacial layer of IMCs and the shear strength of the solder joints.     

Corrosion Behavior of Welded Joints of Al-6Mg Alloy with Trace Scandium Addition

Al-6Mg alloy with trace Sc addition was prepared by means of melting-casting.The samples of the welded joints of Al-6Mg alloy with trace Sc addition were made by method of manual argon-arc welding.Neutral salt spray test was carried out by referring to GB/T10125-1997 and GB6384-1986 practice.Exfoliation testing was carried out in accordance with the method of Al-Mg alloy exfoliation corrosion test.The corrosion behaviors of the welded joints of AlMg alloy with high level of Mg and trace Sc addition were studied.The microstructures of the welded joints were observed by using optical microscope and transmission electron microscope.The corrosion resistance mechanism of the alloy was also involved.This work intended to determine if the welded joints of Al-6Mgalloy with trace Sc addition can have excellent corrosion resistance, when their strength are clearly improved.The results show that trace content of Sc refines the grains of alloys effectively, raises remarkably the corrosion resistance of the welded joints of Al-6Mg alloy with trace Sc addition.The corrosion resistance mechanisms are that there is free of continuous grain boundary precipitation or network which could be susceptible to corrosion in the microstructure of welded joints.     

锡铅焊料中锡的快速测定

本文根据GB10574－89《碘酸钾滴定法测定锡量》的基本原理,对锡铅焊料中锡的测定方法做了进一步探讨,采用盐酸,三氯化铁溶样,铝片还原、碘酸钾滴定的方法,并对还原装置进行了改装。方法易掌握,快速、准确度高,适宜于各种锡铅焊料中锡的测定。测定范围：5．0－95．0％。     

EDTA容量法测定铝合金中的镁

试样以氢氧化钠溶解，使铝、锌转入溶液并与铜、铁、锰、镁等氢氧化物沉淀分离。将沉淀以酸溶解并调节溶液酸度近中性，用DDTC分离铜、铁、锰，然后在PH10的氨性溶液中。以铬黑T为指示剂，用EDTA标准溶液直接滴定镁，测试铝合金中镁的含量。     

Seismic Rehabilitation of Corner RC Beam-Column Joints Using CFRP Composites

In this paper, efficiency and effectiveness of carbon fiber reinforced polymers (CFRPs) in upgrading the shear strength and ductility of seismically deficient corner or knee reinforced concrete beam-column joints have been studied. For this purpose, four as-built corner/knee joints were constructed with no transverse reinforcement, representing extreme case of preseismic code design construction practice of joints and encompassing many existing beam-column corner joints. Out of these four as-built specimens, two specimens were used as baseline specimens (control specimens) and other two were strengthened with CFRP sheets under two different schemes (strengthened specimens). In the first scheme, CFRP sheets were epoxy bonded to joint, beams, and part of the column regions. In the second scheme, however, sheets were epoxy bonded to joint region only but they were effectively prevented against any possible debonding through mechanical anchorages. All these four subassemblages were subjected to cyclic lateral load histories to simulate loading due to earthquake and provide the equivalent of severe earthquake damage. The damaged control specimens were then repaired by filling their cracks through epoxy and externally bonding them with CFRP sheets under the same above two schemes. These repaired specimens were subjected to the similar cyclic lateral load history and their response histories were obtained. Response histories of control, repaired, and strengthened specimens were then compared. The results were compared through hysteretic loops, load-displacement envelopes, column profiles, ductility, and stiffness degradation. The comparison shows that CFRP sheets are very effective in improving shear resistance and deformation capacity of the corner beam-column joints and delaying their stiffness degradation. Shear capacities of control, repaired, and strengthened specimens were also predicted using writers’ published formulation. The predicted shear capacities were in a good agreement with the experimental values.     

Microstructure and Properties Analysis of Laser Welding and Laser Weld Bonding Mg to Al Joints

Laser welding and laser weld bonding (LWB) Mg to Al joints were obtained in different welding parameters. The penetrations and microstructures of these kinds of joints changed with the increasing of pulse laser power density. Both laser welding and LWB Mg to Al joints with the best properties were obtained in conductive welding mode. In laser welding Mg to Al joint, several intermetallics formed at the bottom of the fusion zone, where some cracks were generated. In laser weld bonding Mg to Al joint, the decomposition of the adhesive caused a baffle effect on the diffusion between the Mg and the Al. The intermetallics formed in the middle of the fusion zone, and the thickness of Mg₁₇Al₁₂ layer was approximately 10 to 20 μm and the Mg₂Al₃ layer was less than 5 μm, which influenced the property of the joint less.     

以Si-Cu合金为还原剂的热还原制镁新方法及其热力学分析

结合Si-Fe相图,分析了硅铁热还原制镁(皮江法)反应过程中Si-Fe中形态,结果显示:初始含Si量75%的Si-Fe在1200℃基本处于固态,硅铁热还原制镁还原反应主要为固-固反应,反应过程中,物料间的热量及质量传输较困难,反应难于快速、彻底进行。介绍了采用Si-Cu合金还原剂实现固-液还原的Si-Cu热还原制镁新思路、新方法,结合Si-Cu相图,分析了Si-Cu热还原制镁中Si-Cu的形态,结果显示:Si-Cu热还原制镁时,初始含Si量低于35%的Si-Cu在1200℃几乎全过程保持液态,还原反应基本为固-液反应,反应较易快速、彻底进行。采用热力学分析方法,推演出了Si-Cu热还原制镁的主要反应式、吉布斯自由能估算式,临界反应温度估算式,分析了影响吉布斯自由能、临界反应温度及还原反应热力学可行性的因素,结果显示:Si-Cu热还原制镁反应的热力学临界温度随系统气压降低及Si-Cu中Si含量增加而减小;对应于常规真空硅热还原制镁(皮江法)温度(1473 K)和系统气压(13.3 Pa),Si-Cu合金中的Si含量只需高于0.034%,Si-Cu热还原制镁即具备热力学可行性。     

Assessment of Bridge Expansion Joints Using Long-Term Displacement and Temperature Measurement

A procedure for assessment of bridge expansion joints making use of long-term monitoring data is presented in this paper. Based on the measurement data of expansion joint displacement and bridge temperature, the normal correlation pattern between the effective temperature and thermal movement is first established. Alarms will be raised if a future pattern deviates from this normal pattern. With the established correlation pattern, the expansion joint displacements under the design maximum and minimum temperatures are predicted and compared with the design allowable values for validation. The extreme temperatures for a certain return period are also derived using the measurement data for design verification. Then the annual or daily-average cumulative movements experienced by expansion joints are estimated from the monitoring data for comparison with the expected values in design. Because the service life and interval for replacement of expansion joints rely to a great extent on the cumulative displacements, an accurate prediction of the cumulative displacements will provide a robust basis for determining a reasonable interval for inspection or replacement of expansion joints. The proposed procedure is applied to the assessment of expansion joints in the cable-stayed Ting Kau Bridge with the use of one-year monitoring data.     

Density and viscosity of molten Zn-Al alloys

Different Zn-Al alloys were applied in various hot-dip coating processes, such as galvanizing, GALFAN, GALVALUME, and aluminizing, for corrosion protection. Density and viscosity are two important parameters of the molten alloys in many studies, especially those involving fluid mechanics. However, the experimental data of these two important properties are scarce. Interpolation and extrapolation of experimental data are often necessary. Models that can describe the entire system are needed for the prediction of these properties at different temperatures and with different alloy compositions. Various thermodynamic models were examined in the current study, and the one that provided the best fit to the experimental data of the Zn-Al binary system was introduced.     

Seismic Behavior of Reinforced Concrete Interior Beam-Wide Column Joints Repaired Using FRP

To prevent the casualties that can result from the collapse of earthquake-damaged structures, it is important that structures be rehabilitated as soon as possible. This paper proposes a rapid rehabilitation scheme for repairing moderately damaged reinforced concrete (RC) beam-wide column joints. Four nonseismically detailed interior beam-wide column joints were used as control specimens. All four subassemblages were subjected to similar cyclic lateral displacement to provide the equivalent of severe earthquake damage. The damaged control specimens were then repaired by filling their cracks with epoxy and externally bonding them with carbon-fiber-reinforced polymer (CFRP) sheets and glass-fiber-reinforced polymer (GFRP) sheets. These repaired specimens were then retested and their performance compared with that of the control specimens. This paper demonstrates that the repair of damaged RC beam-wide column joints by using FRP can restore the performance of damaged RC joints with relative ease, suggesting that the repair of beam-column joints is a cost-effective alternative to complete demolition and replacement     

铸造锌铝合金的研究进展及其应用

回顾了锌铝合金的研究历史，并详述了锌铝合金的成分、显微组织与性能的关系，以及变质、晶粒细化、热处理和其它工艺对锌铝合金的性能和组织结构的影响，最后介绍了铸造锌铝合金的应用，并对锌铝合金的发展趋势作了展望。     

高能球磨制备Zn—Al合金

用高能球磨的方法制备锌镉合金粉末．用SEM等方法表征粉末的组织性能。结果表明：在一定的球料比和球磨时间下,在特定助剂的作用下,形成同溶体合金。     

Effect of Tool Offset and Tool Rotational Speed on Enhancing Mechanical Property of Al/Mg Dissimilar FSW Joints

Friction stir welding (FSW) is a promising solid-state joining technique for producing effective welds between Al alloy and Mg alloy. However, previously reported Al/Mg dissimilar FSW joints generally have limited strength or barely any ductility with relatively high strength, which was blamed on the brittle intermetallics formed during welding. In this study, effective joints with comparably high strength (163 MPa) and large elongation (~6 pct) were obtained. Three crucial/weak zones were identified in the welds: (1) Al/Mg bottom interface (BI) zone that resulted from the insufficient materials’ intermixing and interdiffusion; (2) banded structure (BS) zone which contains intermetallic particles possibly formed by constitutional liquation; and (3) softened Al alloy to the retreating side (SAA-RS) zone due to the dissolution and coarsening of the strengthening precipitates. Three fracture modes observed in the tensile specimens perpendicular to the weld seam were found closely related to these zones. Their microstructure evolution with the change of tool rotational speed and tool offset was characterized and the consequent effect on the fracture mode alteration was studied. It turned out that enhancing the strengths of all these zones, but keeping the strength of the SAA lowest, is an effective way for enhancing ductility while keeping comparatively high strength in Al/Mg FSW joints. Also, suggestions for further improving the mechanical property of the Al/Mg dissimilar FSW joints were made accordingly for practical applications.