Cracks can occur in the welded joints of weathering mild steel during the conventional welding process, due to the high phosphorus content. The present work studies the microstructure and mechanical properties of weathering mild steel by friction stir welding (FSW), which makes welding possible at lower temperature. The weathering steels SMA490-AW and SPA-H with different chemical compositions were joined by FSW below the A₁ temperature. The microstructure of the welded joints was observed by scanning electron microscope (SEM) and electron backscatter diffraction (EBSD), and the micro-hardness was assessed corresponding to the various weld regions. The mechanical properties were then assessed by digital image correlation (DIC). The results suggest that the joints with no defects were obtained for both materials (SMA490-AW and SPA-H) and no softening was observed in HAZ. The FSW joints experienced two steps of yield due to the high micro-hardness and strength of weldment. The joint efficiency of SMA490-AW and SPA-H by FSW could be as high as 100%. A sound ductile behavior was observed for both materials, while the SPA-H, also characterized with enhanced anti-corrosion properties, illustrated a more favorable strength and ductile property than SMA490-AW.

由于磷含量高，在常规焊接过程中，耐候低碳钢的焊接接头可能会出现裂纹。目前的工作是通过搅拌摩擦焊 (FSW) 研究耐候低碳钢的微观结构和机械性能，这使得在较低温度下焊接成为可能。具有不同化学成分的耐候钢 SMA490-AW 和 SPA-H 在 A ₁以下通过 FSW 连接温度。通过扫描电子显微镜（SEM）和电子背散射衍射（EBSD）观察焊接接头的显微组织，并根据不同的焊缝区域评估显微硬度。然后通过数字图像相关性 (DIC) 评估机械性能。结果表明，两种材料（SMA490-AW 和 SPA-H）都获得了没有缺陷的接头，并且在 HAZ 中没有观察到软化。由于焊件的高显微硬度和强度，FSW 接头经历了两个屈服阶段。FSW 的 SMA490-AW 和 SPA-H 的联合效率可高达 100%。两种材料均观察到良好的延展性，而 SPA-H 也具有增强的抗腐蚀性能，显示出比 SMA490-AW 更有利的强度和延展性。