One of the methods to achieve local change in material properties when producing high strength parts with tailored mechanical properties is variating temperature histories in the furnace prior to hot stamping. This causes changes in surface layer development of coated steels and thus differences in contact resistances, which determine heat development during the resistance welding process. To get a deeper understanding of the influences, surface layers have on the welding process, parts with temperature histories, typical for industrially manufactured partially hot-stamped parts with aluminum-silicon and zinc coatings were investigated. Static contact resistance was determined; measurements of dynamic resistances in welding process were conducted. Welding current ranges were determined for different heat-treated conditions. No correlation between static contact resistance and welding current range was found; however for Zn coating, the welding current range was moved towards lower welding currents and shrinked for the measured total static contact resistance of about 4000 μΩ. For aluminum-silicon coating, no dependence between welding current range and static contact resistance was evident. For Al-Si-coated steel, a novel criterion, based on the fraction of the resistive phases in the surface layer, determined by metallographic investigations was developed, allowing to determine material joinability.

中文翻译：

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表面层对带有铝硅和锌涂层的部分硬化钢22MnB5电阻点接合能力的影响

在生产具有定制机械性能的高强度零件时，实现材料性能局部变化的一种方法是在热冲压之前改变炉中的温度历史记录。这导致涂层钢表面层发展的变化，从而引起接触电阻的差异，这决定了电阻焊接过程中的热量发展。为了更深入地了解这些影响，研究了表面层对焊接工艺的影响，研究了具有温度历史的零件，这些零件通常用于工业生产的带有铝硅和锌涂层的部分热冲压零件。确定了静态接触电阻；测量了焊接过程中的动态电阻。确定了不同热处理条件下的焊接电流范围。在静态接触电阻和焊接电流范围之间没有发现相关性。但是，对于Zn涂层，焊接电流范围朝较低的焊接电流移动，并且对于测得的总静态接触电阻约为4000μΩ，其焊接电流范围缩小。对于铝硅涂层，焊接电流范围和静态接触电阻之间没有明显关系。对于涂有铝硅的钢，基于金相研究确定了一种基于表面层中电阻相分数的新标准，从而确定了材料的可连接性。焊接电流范围和静态接触电阻之间没有明显关系。对于涂有铝硅的钢，基于金相研究确定了一种基于表面层中电阻相分数的新标准，从而确定了材料的可连接性。焊接电流范围和静态接触电阻之间没有明显关系。对于涂有铝硅的钢，基于金相研究确定了一种基于表面层中电阻相分数的新标准，从而确定了材料的可连接性。