汽車製造工業中，為了因應先進高強度鋼中各類不同新型鋼種的點銲需求，一種藉由施加多段式銲接電流的電阻點銲新製程正逐步發展當中。本研究利用低、中、高三種入熱量所對應的銲接電流分別對先進高強度鋼中的雙相鋼DP980以及熱沖壓硼鋼15B22施加單段式與兩段式點銲製程，並進行拉伸剪切試驗、銲點熔核大小、硬度分佈、顯微組織以及失效模式等實驗與分析，以調查該兩種材料在實施兩段式點銲製程後的機械性質變化，同時探討其變化的原因與機制，並與傳統單段式點銲製程作比較。

研究結果顯示，銲核尺寸皆隨著入熱量增加而提升。而DP980在兩段式點銲中施加低、中入熱量時具有比單段式點銲更高的拉伸剪切負載及破壞能，在高入熱量時拉伸剪切負載及破壞能卻與單段式點銲幾乎相同。15B22則在兩段式點銲的中、高入熱量具有比單段式點銲明顯更低的拉伸剪切負載及破壞能。由硬度分佈及顯微組織可以得知，造成兩段式點銲機械性質下降的主要原因是入熱量增加而導致材料中的軟化效應提升所致。再由失效模式分析發現點銲試件更容易由軟化的區域破壞。最後比較DP980與15B22的機械性質結果可以推論15B22由於具有較高含量的麻田散鐵而較容易受到軟化效應的影響，使得該材料在兩段式點銲中機械性質下降的現象比DP980更為明顯。

Double pulse resistance spot welding process by applying a second step welding current is a new pathway to alter the mechanical properties for advanced high strength steels. Herein, the resistance spot welding (RSW) of dual phase DP980 and hot stamped boron steel 15B22 by one-step and two-step welding with different welding currents is investigated. The results of the tensile–shear test, size of the weld nugget, hardness distribution, microstructure, and failure mode of different welding parameters are analyzed. The weldment of the two-step RSW with a higher heat input exhibits a lower tensile–shear load and lower fracture energy when the size of the weld nugget is large. The microstructural study reveals the appearance of a partially melted zone and sub-critical heat affected zone in the weldment where the fracture readily occurred. Thus, the two-step RSW process weakens the strength of the sample, which is attributed to the partial softening in the weldment due to the higher heat input.

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