| Summary: | 碩士 === 國立雲林科技大學 === 機械工程系 === 107 === 7075 high-strength aluminum alloy has excellent mechanical property, and is widely used in aerospace industry, transportation and defense industry. Although 7075 alluminum alloy has the best mechanical property, the welding process will be accompanied by stress corrosion, heat-reactivity (thermosensitivity) and poor weetability of filler alloy, which will cause the mechanical property and structure to be deteriorated. Therefore, high-reliable low temperature bonding is critical to the development of 7075 alluminum alloy applications. The purpose of the research is to use ultrasonic assisted low-temperture transient liquid diffusion bonding with high-reliability bonding to eliminate the limitation of long-term compression and heating of solid diffusion bonding and overcome the problem of long processing time of traditional transient liquid diffusion bonding. Sn, Sn-9Zn, Sn-8Zn-3Bi, Sn-8Zn-3Bi-4Ti and Sn-8Zn-3Bi-4Ti-0.1Y are the solder alloys used in this research. Besides discussing the addition of alloying elements have an impact on the wettability of 7075 aluminum alloy, metallographic test, solidus and liquidus temperature and mechanical property of solder alloys are analyzed in this study. The transient liquid diffusion bonding of 7075 high-strength aluminum alloy is performed by mechanical activated—thermal diffusion and ultrasonic-assisted high-speed isothermal coagulation, respectively.
The addition of 9% zinc to tin can lower the fusion pointof alloys to about 198℃. If 3% Bi, 4% Ti and 0.1% Y are added, it has no significant influence on melting point. Nevertheless, zinc increases apparently after the addition of Bi, Ti and Y. Using mechanical activated—thermal diffusion to carry out solid liquid interdiffusion bonding. At the reaction temperature of 300℃, the aluminum largely melted into the weld. As the reaction time increases, the junction shear strength decreases. After holding the temperature for 100 hours, tin in the weld disappeared, and was completely replaced by aluminum. Use ultrasonic-assisted high-speed isothermal coagulation to bond 7075 aluminum alloy. Using ultrasonic wave at the temperature of 250℃ from one second to 30 seconds, the aluminum dissolved in the weld as the time increases. The addition of zinc can also accelerate the dissolution of aluminum. The addition elements such as Bi, Ti and Y have no significant impact on the dissolution rate of aluminum. However, the addition of these elements can obviously improve the oxidation resistance of the filler alloys. Ultrasonic soldering filler alloy directly wet 7075 aluminum alloy, with the amplitude at 65% and 100%, and using ultrasonic wave on aluminum alloy for 30 seconds to discuss the bonding effect of different soldering alloys. The result shows that zinc solder has the best bonding effect, and the Sn-8Zn-3Bi-4Ti-0.1Y solder alloy is the worst.
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