可控氧化性气氛下光纤激光拼焊铝硅镀层热成形钢接头组织性能调控机制

铝硅镀层（AlSi10）热成形钢的激光拼焊板广泛用于汽车车身安全结构件制造，对其进行激光拼焊时铝硅镀层熔化后将进入焊接熔池，导致焊缝局部区域因固溶铝富集而形成恶化强塑性的δ铁素体。预研发现，在含CO2气氛下进行该类型钢激光焊接时，可显著促进熔池内固溶铝转化为纳米尺寸氧化铝，从而降低焊缝中δ铁素体含量。基于此，提出“可控氧化性气氛（x%Ar+(100-x)%CO2）下光纤激光焊接铝硅镀层热成形钢”的新思路，通过对激光作用下铝硅镀层与CO2在熔池表面的反应机制、固溶铝在熔池内的氧化动力学及其对非平衡凝固及固态相变的影响、焊接工艺-显微组织-焊接质量之间本质关系、接头强塑化机制等方面的研究，实现铝在焊缝处的“无害化残留”，揭示在可控氧化性气氛光纤激光焊接铝硅镀层热成形钢接头组织性能调控新机制。项目的成功实施，将有望为“焊前免去除铝硅镀层”激光焊接的热成形部件“两步法”制造提供科学依据及技术方向。

Laser tailor-welded blanks (TWBs) of Al-Si coated (AlSi10) press-hardened steel (PHS) has been widely used in automotive safety structural parts manufacturing. However, solid solution aluminum had a local enrichment in the laser welded seam to form δ ferrite, due to the presence of Al-Si coating. It will deteriorate the strength and plasticity of PHS welded joints. We have found that the content of solid solution aluminum and δ ferrite in the welded seam was reduced as the formation of Al2O3, with CO2 shielding atmosphere during laser welding of Al-Si coated PHS sheets. Based on this, a novel idea is proposed to do the laser welding of Al-Si coated PHS sheet under controllable oxidizing atmosphere (x% Ar+(100-x)% CO2). In this project, We will focus on four issues as follows: Reaction mechanism between Al-Si coating and CO2 on the surface of laser welding pool; oxidation kinetics of solid solution aluminium in laser welding pool and its influence on non-equilibrium solidification and solid-state transformation; essential relationship between welding process, microstructure and welding quality; strengthening and plasticizing mechanism of weld joint. A new regulation mechanism for the microstructure and properties of welded joint will be revealed, which is suitable for laser welding Al-Si coated PHS under controlled oxidation atmosphere. If the project is successfully completed, it will provide scientific basis and technical direction for the realization of "two-step" manufacturing of laser-welded PHS parts without removing Al-Si coating before welding.