Uniform Intermetallic Compound Research Articles

Laser welding-brazing under temporal and spatial power modulation for dissimilar materials AA6061 to Ti6Al4V joints

A novel laser welding-brazing process with temporal and spatial power modulation was firstly reported to join dissimilar alloys of AA6061 and Ti6Al4V with medium thickness. The power modulation was achieved by changing laser power as the same time as laser beam oscillating. A sound welded-brazed joint with relatively uniform intermetallic compound morphology along the Ti/Al interface was obtained. A multi-physical model was also developed and utilized to understand the underlying mechanism of the benefit of the temporal and spatial power modulation. It was found that the temperature gradient along the Ti/Al interface was reduced effectively by using this novel process.

Deep-penetration welding-brazing of aluminum/steel dissimilar metal using laser-MIG arc hybrid heat source

Deep-penetration welding-brazing process without gap of steel/aluminum dissimilar metal butt joint with a thickness of 4 and 6 mm was achieved using laser-MIG hybrid heat source. The welding parameters were optimized to obtain a sound joint and the microstructure of the interfacial layer was observed by scanning electron microscopy (SEM) and experimental validation. The joint temperature distribution of three welding methods: MIG welding-brazing, laser welding-brazing, and laser-MIG hybrid deep-penetration welding-brazing were investigated by finite element method (FEM) numerical simulation. Moreover, the effect of laser deflection angle on the temperature distribution of the laser-MIG deep-penetration welding-brazed joint was investigated. The results indicated that the temperature distribution of laser-MIG hybrid deep-penetration welding-brazed joint was more uniform than MIG welding-brazing and laser welding-brazing. The temperature of the lower part of the joint was increased, which was beneficial to improve wetting and spreading of the liquid metal on the stainless steel and obtain better weld formation. In the laser-MIG hybrid deep-penetration welding-brazing process, the temperature of the lower part of the joint interface and the interface temperature gradient could be improved by adjusting the laser deflection angle, which was beneficial to the formation of uniform intermetallic compound layer. Typical welding-brazing joint characteristic with the thickness of 4 mm using laser-MIG hybrid heat source was found. The main phases of interface layer compounds were composed of Fe4Al13 and Al8Fe2Si, and the weld metal consisted of α-Al and Al-Si eutectic. The 6-mm steel/aluminum joint was also achieved by using laser-MIG hybrid heat source, but some cracks at the interface were observed.

Minor P Doping to Effectively Suppress IMC Growth in Solder Joints with Electroplated Co(P) Metallization

Electrodeposited Co(P) layers with three different P contents (0.5 wt.%, 0.8 wt.%, and 2 wt.%) have been coated on Cu substrates by adding minor amounts of sodium hypophosphite to the Co plating bath. These hcp-Co(P) coatings exhibited highly preferred (002) orientation. Solid-state interfacial reactions of 6-μm-thick Co(P)/Cu with pure Sn were conducted at temperatures of 160°C to 210°C. In the Sn/Co-0.5 wt.%P/Cu reactions, a uniform intermetallic compound (IMC) layer of CoSn3 was formed and its thickness increased linearly with aging time. Most importantly, the IMC growth was significantly inhibited compared with that of the Sn/Co/Cu reaction without P doping. When the P content was increased to 0.8 wt.%, the formed phases contained not only CoSn3 but also metastable CoSn4, and the suppression effect became stronger. The IMC growth rate at 180°C was decreased by 95% in comparison with the pure Co case. The growth rate with Co-2 wt.%P was between that observed for the 0.5 wt.% and 0.8 wt.% P compositions, so the IMC growth kinetics of the Co coatings with 0.5 wt.% and 0.8 wt.% P compositions were systematically investigated. Minor P doping in the Co deposit greatly suppressed the IMC growth.

Al/Cu Dissimilar Friction Stir Welding with Ni, Ti, and Zn Foil as the Interlayer for Flow Control, Enhancing Mechanical and Metallurgical Properties

This research investigates the effects of Ni, Ti, and Zn foil as interlayer, inserted between the faying edges of Al and Cu plates, for controlled intermetallic compound (IMC) formation. The weld tensile strength with Ti and Zn as interlayer is superior to Al base metal strength. This is due to controlled flow of IMCs by diffused Ti interlayer and thin, continuous, and uniform IMC formation in the case of Zn interlayer. Improved flexural stress was observed with interlayer. Weld microhardness varied with different interlayers and purely depends on IMCs present at the indentation point, flow of IMCs, and interlayer hardness. Specimens with interlayer failed at the interface of the nugget and thermomechanical-affected zone (TMAZ) with complete and broken three-dimensional (3-D) grains, indicating transgranular fracture. Phase analysis revealed that Al/Cu IMCs are impeded by Ni and Ti interlayer. The minor binary and ternary IMC phases form adjacent to the interlayer due to diffusion of the material with Al/Cu. Line scan and elemental mapping indicate thin, continuous, and uniform IMCs with enhanced weld metallurgical and mechanical properties for the joints with Zn interlayer. Macrostructural analysis revealed IMC flow variations with and without interlayer. Variation in grain size at different zones is also observed for different interlayers.

Influence of rapid solidification on microstructure, thermodynamic characteristic and the mechanical properties of solder/Cu joints of Sn–9Zn alloy

Rapidly solidified Sn–9Zn alloy foils were prepared by the melt-spinning method. The effects of rapid solidification process on the microstructure, thermodynamic characteristic, electrochemical corrosion properties and spreading properties of Sn–9Zn solder alloys were analyzed. The mechanical properties and fracture behaviors of the solder/Cu joints were also investigated. The results showed that the rapid solidification process could obviously refine the solidification structure of Sn–9Zn alloy and a fine netlike dendrite structure was formed due to the rapid branch of Sn phase. The Zn phase was distributed in Sn matrix in granular form. After rapid solidification, the pasty range decreased from 7K to 4K, the wettability was modestly improved, and the corrosion resistance of the rapid solidified alloy was improved significantly. The tensile shear strengths of the joints using the rapidly solidified solder were obviously higher than that of the joints using the as-solidified solders result from the formation of fine-grained intermetallic compound (IMC) with a needle pattern and more uniform IMC layer at the interface.

Interfacial reactions of high-temperature Zn–Sn solders with Ni substrate

The interfacial reactions of Ni substrate with various high-temperature Zn–xSn (x=20, 30, 40, and 50wt%) solders were studied through the microstructural observation and reaction kinetics analysis of interfacial products. Regarding liquid/solid reactions at temperatures of 380°C to 420°C, only one uniform intermetallic compound (IMC), γ-Ni5Zn21, was formed on the interface. In the Zn–20Sn/Ni reacted at 400°C, the Ni5Zn21 layer demonstrated an unusually porous structure that grew rapidly; the average thickness reached ∼140μm after a reaction time of 1h. Specially, the layer exhibited a linear growth correlating to the reaction time. In contrast, the specimens with the Sn content above 30wt% exhibited a considerably lower Ni5Zn21 growth rate, following a parabolic relationship. Additionally, the Ni5Zn21 microstructure was relatively denser. Microstructural variations could be responsible for the different growth kinetics among the Zn–Sn/Ni couples. The Zn–Sn/Ni solid/solid interfacial reactions were also examined at 150–170°C. The Ni5Zn21 layer revealed a linear growth relationship for all the couples. This study determines the relevant growth kinetic parameters, and then discusses the possible growth mechanisms.

Laser Irradiation on Tin Electroplating and Whisker Suppressibility

Tin electroplating with its excellent solderability and low cost performance is garnering attention as a lead-free technology. However, tin electroplated film is plagued with the issue of whisker formation. In this research, in order to suppress the whisker formation, the effect of laser irradiation on tin electroplated film onto a phosphor bronze substrate was studied by scanning electron microscopy and focused ion beam microscopy. Whiskers and nodules were generated on the surface of the tin electroplated film for a short time after electroplating. However, laser irradiated specimens showed no whiskers as well as nodules. This whisker suppression is attributable to the formation of thinly uniform intermetallic compound layer. Moreover, the solderability of the laser irradiated specimen was superior to that of the reflow specimen. These results demonstrated the effectiveness of laser treatment.

Solder Characteristics of a Rapidly Solidified Sn-9Zn-0.1Cr Alloy and Mechanical Properties of Cu/Solder/Cu Joints

Rapidly solidified Sn-9Zn-0.1Cr alloy foils were obtained by the melt-spinning method. The solder characteristics of this rapidly solidified alloy were analyzed and compared with those of as-solidified Sn-9Zn and Sn-9Zn-0.1Cr alloys. The mechanical properties of Cu/solder/Cu joints obtained using these alloys were comparatively investigated. Compared with the as-solidified Sn-9Zn and Sn-9Zn-0.1Cr alloys, the melting point of the rapidly solidified Sn-9Zn-0.1Cr alloy was lower by about 9°C and its wettability was better. The microstructure of the soldering seam was notably fine and the intermetallic compound (IMC) layer became relatively uniform using the rapidly solidified Sn-9Zn-0.1Cr solder. The tensile shear strengths of the joints using the rapidly solidified solder were markedly higher than those of the joints using the as-solidified solders. The former exhibited good solderability and excellent joint strength. The improved properties of the joints might result from the formation of fine-grained IMCs with a needle pattern and more uniform IMC layer at the interface.