Abstract
Brazing joints of Ti/Ti under ultrasonic vibration (USV) and compression load were investigated using optimized and modified filler alloys of Al-Si-Cu-(Ni)-(Sr) group prepared in the lab. Preliminary trails at semisolid to liquid states were conducted using the ready Al-Si-Cu-(Mg) alloy as a filler, then the brazing cycle was redesigned and enhanced according to the microstructural observations of the produced joints. USV assisted brazing at the semisolid state of low solid fraction was able to produce joints with round silicon morphology and granular α−Al, while at a high solid fraction, USV was only able to affect the silicon and intermetallic particles. Applying a compression load after ultrasonic vibration, at a designed solid fraction, was proved to be a successful technique for improving the quality of the joints by reducing the porosity, enhancing the soundness of the joint, and the diffusion at the interface. Based on alloy composition and the improved brazing cycle, joints of thin intermetallic layer and high shear strength (of 93 MPa average value) were achieved. The microstructures and the mechanical behavior were discussed based on the filler compositions and brazing parameters.
Highlights
In the previous work [1], a detailed insight into a brazing process that combined initial load and ultrasonic vibration (USV) was presented
At a high solid fraction (0.73–0.75) under F0-1 brazing condition, the followed brazing cycle (F0-1) was capable of affecting the eutectic silicon and the intermetallic compounds favoring the formation of the round morphology, but USV was not capable of refining the primary grains of Al (Figure 9a)
Increasing temperature/reducing solid fraction enhanced the effect of USV
Summary
In the previous work [1], a detailed insight into a brazing process that combined initial load and ultrasonic vibration (USV) was presented. The brazed joints using Al-13Si were characterized by an acicular morphology of the eutectic silicon and a long needle morphology of Fe intermetallic as a result of the low cooling speed and filler composition To address those microstructures issues, modified filler alloys and/or optimized brazing cycle should be considered, where the formation of the harmful phases can be reduced or eliminated. It was found that brazing temperature around the solidus point has less effect on the formation of the harmful microstructures within the joint, in addition, the formed intermetallic at the interface was minimum at relatively high Si content [1]. The additions of Ni and Sr in the Al-Si-Cu(Ni)-(Sr) filler system were evaluated and the resulted microstructures, interface reactions, and strengths were discussed
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