Effect of Microstructure on Joint Strength of Fe/Al Resistance Spot Welding for Multi-Material Components

The effects of welding conditions such as the electrode type and welding current were investigated on the microstructure and joint strength of the resistance weld of A5052 and GA590. The reaction layer formed at the joint interface was inferred to consist of Fe-Al based intermetallic compounds (IMCs) which are FeAl, FeAl2, Fe2Al5 and FeAl3 by quantitative analysis. Although the thickness of the IMCs layer decreased from the center of the nugget towards the edge of it. When the DR type electrode was used, the cross tensile force became higher than those of the joints formed with the R type one. This is because the thickness of the reaction layer formed at the nugget end of A5052 was thin in the case of the DR type electrode. Also, it was found that cross tensile force increases when the thickness of the reaction layer is thin by multiple regression analysis.

Deformation behavior of steel-to-aluminum tailor blanks made by laser/MIG hybrid and cold metal transfer brazing methods

In this paper, dual phase steel (DP780) and AA2024-T3 aluminum sheets were successfully butt-welded together utilizing laser/MIG hybrid and cold metal transfer (CMT) brazing methods. A comparative study was conducted between the brazed joints produced by both methods in terms of wetting length, intermetallic compounds (IMCs) layer thickness, fracture position, and fracture mode. The results of testing showed that the produced joints from each method introduced significantly different deformation behavior. In addition, better wetting length and lower IMCs layer thickness are not the only factors that improve the mechanical behavior of brazed joints. The susceptibility of the aluminum base metal and time of exposure to the heat sources during joining process are also important.

Effects of Helium Addition to Ar-Based Shielding Gas on the Lap-Joint Performance of 5052 Aluminum Alloy to Galvanized Steel Sheet during the MIG Weld-Brazing Process

In the metal inert gas (MIG) weld-brazing process, the lap-joint welds between 5052 aluminum alloy and automotive galvanized steel sheet were achieved employing an automatic MIG welding machine. The different percentage of helium (He) gas addition to pure argon (Ar) shielding gas was selected to investigate the performance of lap-joint welds such as appearance of weld bead surface, weld bead geometry, microstructure, tensile strength, fracture surface of welds and thickness of intermetallic compounds (IMCs) layer between the dissimilar materials in the brazing zone. The results showed that the lap-joint welds produced by adding 5% and 10% He gas to Ar shielding gas were provided with better performance of specimens. The average tensile strength of lap-joint welds between 5052 aluminum alloy and automotive galvanized steel sheet is 206.23 MPa. In additions, the amount of porosity in the fusion zone that specimens produced by using 10% He addition to Ar-based shielding gas is less than others. It can be found that the thickness of IMCs layer between the weld bead and automotive galvanized steel sheet from 3.30 μm to 4.90 μm.

Laser-CMT Hybrid Welding-Brazing of Al/Steel Butt Joint: Weld Formation, Intermetallic Compounds, and Mechanical Properties

6A01-T5 aluminum alloy and SUS301L-DLT austenitic stainless steel sheets were welded by a laser-cold metal transfer (CMT) hybrid welding-brazing method with ER5183 filler wire. We researched the weld forming, intermetallic compounds, and mechanical character, which are influenced by laser power, wire feeding speed, and welding speed. Well-formed joints with uniformly distributed interface layers were obtained under certain parameters. The spreading and wetting distance on the steel upper surface increased initially and then decreased as the laser power increased, and increased progressively as the wire feeding speed increased or welding speed decreased. There were both Fe2Al5 and Fe4Al13 in the interfacial intermetallic compounds (IMCs) layer. The thickness was controlled to within 2.0–6.9 µm. The thickness of the IMCs layer increased as the heat input increased; however, the increasing rate decreased gradually. The tensile strength of the joints was not only completely dependent on the thickness of the IMCs, but also on the spreading and wetting distance on the steel surface. The highest tensile strength could reach up to 188.7 MPa, which is about 77.1% of that of the base aluminum alloy. The tensile sample fracture occurred at the IMCs layer, and regional metallurgical bonding happened in the interface layer.

Influence of Thermal Aging on Microstructure and Property of Gold Alloy Joint Soldered by Sn-based Solder

As an undisputed material of choice to guarantee reliability in a broad range of high performance and safety-critical applications in the electrical contacts and connectors, AuAgCu alloy was soldered with Ag-plated Cu wire using Sn-based solder. To clarify the embrittlement and strength reduction of the gold soldered joint, the microstructure and its influence on the macroand micro-mechanical properties of the soldered joint under various thermal aging conditions were studied. The result indicated that, taking the mechanical property consideration alone, Sn-based solder could be used to join AuAgCu alloy. Different from the embrittlement and strength reduction of the soldered joint of pure gold, although the brittle fracture features appeared in mechanical test of the soldered joints, the shear strength of soldered joint after thermal aging at 125 °C almost did not decrease in comparison with that before thermal aging. Nevertheless, too high temperature and long time still had bad influence on mechanical properties. Otherwise, thermal aging had a large effect on the IMCs layer, as aging temperature elevated and aging time increased, IMCs layer became thicker, more complex components and multiply-sublayers structure with different microhardness. The study provides a fundamental understanding for gold alloy soldering.

The Effects of Gallium Additions on the Microstructure of Lead-Free Solder Materials: A Short Review

This paper reviews the results of gallium (Ga) additions on the properties of Lead (Pb)-free solder alloys in terms of the solderability, microstructure and mechanical properties. Throughout the review, it is proven that when 0.5% of Ga is added, the shear force is improved and the grain size of the solder has refined remarkably. Besides, the addition of Ga has significantly suppressed the interfacial intermetallic compounds (IMCs) formation at solder/Copper substrate interface. This is caused by the formation of the Cu2Ga phase around the joint surface during solidification which decrease the growth rate of the IMCs layer. In fact, the enhancement in the mechanical aspect can also be affiliated with the improvement of the IMCs of the solder due to the addition of Ga. Moreover, Ga element also added to act as solid solution strengthening in β-Sn matrix. Furthermore, the addition of Ga element definitely decreases the melting temperature of Pb-free solder in Sn-0.7Cu Pb-free solder. As Ga addition also improve the oxidation resistance and reduce the surface tension of the solder, thus the solderability of the Pb-free solder alloys is slightly improved.