| Summary: | 碩士 === 國立高雄應用科技大學 === 機械與精密工程研究所 === 99 === In recent years, the application needs of high performance and light weight metal material increase recently such as aluminum alloy that has high strength, light weight and high corrosion resistance properties. Generally producing complex structural parts are mostly dominated by welding processes; however, it is difficult to weld high strength aluminum alloy in aluminum extrusion industry. The welding of high strength aluminum alloy is still not easy, especially for extruded material with separating flow characteristics. This study tents to find the best welding conditions for high strength aluminum alloy which can be used in the actual production line.
The study used simple type round billets for pressing and joining experiments where the studied material is high strength aluminum alloy 7075 under constant pressure and temperature conditions. Two kinds of condition are varied, namely: the pressing fixture with initial gap or not, and the condition in protection environment or not. In order to investigate the joining results in the main body and the flash part of specimen, the microstructure, welding strength and oxidation percentage have been analyzed by using SEM/EDS and mechanical testing device.
Research results show that the specimen in main body has better mechanical properties, such as tensile strength and hardness in protection environment than without protection environment. Specimen in flash part has the best mechanical properties. Sample element analysis by EDS found that the main body failed to weld due to contain high oxygen percentage in contact interface. Hardness analysis show that the hardness value is about 77.6HV in the main body near the welding seam without environment protection, and 94.51HV in the main body near the welding seam with environment protection, and 106.59HV in the welding seam in the flash part which reached two times of the initial Al7075 billet. Through the tensile tests for welding seam, the tensile strength in main body is approximately 54.34MPa without protection environment, 58.11MPa with protection environment. The tensile strength in flash part is about 410.32MPa which is up to 85.19% of initial Al7075 billet.
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