| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 101 === This study investigated the laser weldability and welding process window of three different copper sheets: the oxygen-free copper (OFC), OFC coated with nickel or OFC coated with tin, on the SPCC (thickness 0.2mm) where Lap-Joint welding by laser were performed. The mechanical properties test and microstructure analysis of the welding joint were used to examine the degree of conductivity, strength and microstructure characteristics in different materials and parameters. The welding ability of corrosion resistance at general environmental was analyzed by electrochemical test. Finally, the optimum welding process window as laser welding of copper sheet would be obtained.
As the results of the experiment, the base material – OFC coated with tin had the maximum laser absorptivity. At the beginning of welding, it would form the copper-tin alloy with low melting point at the weld fusion zone, so the heat could be effectively passed down to SPCC. Thus, OFC coated with tin would achieve satisfactory laser weldability among three different copper sheets. The molten zone was raised up with the increasing defocus distance to expand the process window and spot area gradually. There were optimum effect of welding when the defocuses distance were at 9mm and 10mm.
As the analysis of the experiment, there was the maximum welding diameter 955um under defocused 9mm, pulse width 10ms, peak power 10kW, shielding gas (Ar) flow rate 10L/min, which would have the maximum tensile force of 74.3N and minimum resistance of 0.217 mΩ. But there was poor corrosion resistance due to the content of iron ions with 38% at diffusion layer which would cause the selective corrosion easily.
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