| Summary: | 碩士 === 國立中興大學 === 材料工程學研究所 === 92 === Automotive weight reduction contributes to the reduction of CO2 discharging. Magnesium alloys are attractive for structural components in transportation applications due to their light weight and high specific strength.
The spot welding skill is one of the important procedures to assemble automobile, by adding the loading of electrodes and producing resistance heat. However, the spot welding research about the magnesium alloy are limited. In this study, two kinds with different head morphology are used for the welding. The plane-electrode will cause the residual copper on welding surface. The spherical-electrode will cause the residual copper at the central region of weld surface, but left copper-magnesium alloy at periphery of weld surface.
After welding, nugget size is not related to the electrodes loading, but related to welding current and electrode form. The nugget size of the welded specimen by plane-electrode will increase with welding current apparently, but the nugget size of the welded specimen by spherical-electrode has no apparently variation following welding current. The microstructure changes of HAZ and fusion zone after welding are also related to welding current and electrode form, but not related to electrode loading. The corrosion behavior of welding surface was investigated in 3.5wt% NaCl(aq) at room temperature. Electrochemical testing results confirm the combined effects of the residual copper on the welding surface. The Icorr value of welding surface increases with welding current. The copper remains on the welding surface will reduce the corrosive resistance of welding surface. But when after welding machining the welding surface with the #400 sandpaper can increase the corrosive resistance of welding surface effectively.
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