| Summary: | 碩士 === 國立臺灣師範大學 === 工業教育研究所 === 89 === The characteristics were explored during resistance spot welding a commercial aluminum alloy 7075 in this study. The 7075 aluminum alloy sheets of 1.5mm gauges and in T6 condition were used in all experiments. Single spot weld was made on the specimens using a single-phase AC welding machine. The welding parameters were changed systematically, including welding current, electrode force and holding time. Metallographic studies were made by optical and scanning electron microscopy and microhardness was measured across the sectioned weldment using a hardness tester. The fluctuation behaviors of tensile-shear strength after welding have been analyzed by applying the Weibull distrbution function.
According to the experimental results, the proper welding parameters were 2.2kg/cm2electrode force,14.2kA welding current and 19 cycles of holding time. The hardness in the nugget is lowest,about Hv70,and the base 7075 alloy is highest. During tensile-shear testing, both nugget and heat affected zones (HAZ) are the regions for the fracture occurring. On the other hand, the reliability properties, such as tensile-shear strength distributions, reliability probabilities and minimum life, were calculated and predicted. All the tested results of Weibull modulus, m, are higher than one and the failure mode is‵wear-out′type.
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