AZ31镁合金摩擦搅拌焊在慢拉伸应力腐蚀过程中的组织演化和氢致延迟开裂

摘要

研究AZ31镁合金摩擦搅拌焊组织的演化，包括织构和断口变化。利用中子衍射仪测量织构。利用光学显微镜和扫描电子显微镜观察应力腐蚀开裂(SCC)样品的金相及断口形貌。利用X射线衍射仪研究SCC样品的断口表面结构。结果表明，在母材表面形成了明显的基面织构。然而，搅拌区晶粒发生了基面旋转，大多数晶粒的基面沿着焊接方向倾斜25°。在慢拉伸应力作用下，在空气和侵蚀性溶液中分别形成了羽毛状孪晶和氢化物。在溶液中，穿晶裂纹扩展，最终断裂在回转侧。在断口表面存在的氢化物表明镁合金应力腐蚀可能存在氢致延迟开裂机制。%Evolution of microstructure including texture and fractography in a friction-stir welded (FSW) AZ31 magnesium alloy was investigated. The texture was measured using a neutron diffractometer. The microstructure and fractography of stress corrosion cracking (SCC) samples were observed by optical and scanning electron microscopy, respectively. An X-ray diffraction study was carried out on the fractured surfaces of the SCC specimens. The results indicated that a strong basal fiber was formed on the base material, whereas the grains in the stir zone were reoriented with their most basal planes tilted 25º to the welding direction. Feather-like twins and hydride formed under slow strain rate tensile (SSRT) stress in air and aggressive solutions, respectively. Transgranular cracks propagated and finally failed on the retreating side in the solution. The hydride phase confirmed to sit on the fracture surface demonstrated the delayed hydride cracking (DHC) mechanism of the alloy.