In the automotive industry, the demand for reduced vehicle weight, improved safety and enhanced crashworthiness qualities continues to rise which introduces the need for parts with tailored properties. This demand can be met by employing tailor-welded blanks which are made of two or more types of press-hardened steels that are laser welded together and then hot-stamped to produce highly optimized parts for use in vehicle body-in-white applications. The most commonly used press-hardened steel for high strength applications is the Al-Si coated 22MnB5 grade steel that has a strength of around 1500 MPa in the hot-stamped condition. Although the Al-Si coating offers excellent barrier protection against oxidation and decarburization during hot-stamping, the Al-Si coating proves to be problematic during laser welding as it melts and mixes into the weld pool increasing the Al-content in the fusion zone, which promotes the formation of ferrite during the heat-treatment stage of hot-stamping, resulting in a dual-phase fusion zone microstructure that consists of ferrite grains embedded in a martensitic matrix. The presence of the softer ferrite phase has been shown to be the principal reason for premature failure of hot-stamped laser-welded joints. Currently, this issue is resolved by an additional, and relatively costly, manufacturing step that involves the laser ablation of the Al-Si coating prior to welding. The present work shows that this step can be eliminated from the manufacturing process by welding Al-Si coated 22MnB5 steel through a colloidal graphite coating which results in the in-situ ablation of the Al-Si coating during welding. This changes the alloying chemistry of the fusion zone which affects the resulting morphology by preventing ferrite formation which improves the mechanical properties of the weld. Failure in these welded samples was successfully shifted from the fusion zone, where it normally occurs, to the base material.

在汽车工业中，对减轻车辆重量，提高安全性和提高防撞性能的需求不断增长，这导致需要具有定制性能的零件。通过使用由两种或更多种类型的冲压硬化钢制成的拼焊板可以满足这种需求，这些冲压硬化钢被激光焊接在一起，然后进行热冲压以生产用于汽车白车身应用的高度优化的零件。对于高强度应用，最常用的压淬钢是Al-Si涂层的22MnB5级钢，在热压状态下的强度约为1500 MPa。尽管Al-Si涂层在热压印过程中提供了出色的防氧化和脱碳屏障保护，事实证明，Al-Si涂层在激光焊接过程中存在问题，因为它熔化并混入焊缝中，增加了熔合区中的Al含量，从而在热冲压的热处理阶段促进了铁素体的形成，从而导致双相熔合区显微组织，由嵌入马氏体基体中的铁素体晶粒组成。业已证明，较软的铁素体相的存在是热冲压激光焊接接头过早失效的主要原因。当前，该问题通过额外的且相对昂贵的制造步骤来解决，该制造步骤包括在焊接之前对Al-Si涂层进行激光烧蚀。目前的工作表明，通过将铝硅涂层的22MnB5钢通过胶态石墨涂层进行焊接，可以在制造过程中省去这一步骤，从而在焊接过程中对铝硅涂层进行原位烧蚀。这改变了熔合区的合金化学性质，通过防止形成铁素体而影响了最终的形貌，从而改善了焊接的机械性能。这些焊接样品的失效已成功地从通常发生的融合区转移到了基础材料上。