AZ91筒形件旋压的组织衍化及微纳力学性能

Microstructure evolution and micro/nano mechanical properties of AZ91 magnesium alloy tube by spinning

摘要:

本文采用强力正旋的方式对AZ91镁合金筒形件进行多道次旋压，通过光学显微镜(OM)和配有电子背散射衍射和能谱的扫描电子显微镜(SEM-EBSD-EDS)对不同旋压道次的微观组织衍化进行观察，结合EDS和X-Ray衍射仪（XRD）对筒形件的物相进行分析，通过纳米压痕试验仪对不同旋压道次镁合金的微区力学性能进行测试。研究结果表明：当AZ91镁合金筒形件的壁厚减薄率达到88.3%时，表面成形良好，无裂纹、褶皱产生；在旋压的初期，主要为外壁镁合金发生塑性变形，随着旋压变形量的增加，筒形件内外壁镁合金变形趋于一致，组织均匀，脆性相Mg17Al12发生破碎，呈流线形弥散地分布在镁合金内部，同时镁合金晶粒也得到细化，并发生动态再结晶；随着变形量的增加，筒形件的强度提高，硬度最高可达1.036 GPa，强化方式主要为第二相弥散强化和细晶强化。

Abstract:

In this study, multi-pass spinning of AZ91 magnesium alloy tube was conducted by power forward spinning. The microstructural evolution, phaseStransformation and micro mechanical properties were examined by opticalSmicroscope, SEM-EBSD-EDS, and nano-indentation tests. The results show that when the wall thickness of AZ91 magnesium alloy tube reduced by 88.33%, the surface was well formed without cracks or folds. In the initial stage of spinning, plastic deformation mainly occurred on the outer surface of magnesium alloy. With the spinning deformation increased, the deformation of inner and outer surface tended to be consistent. The brittle phase Mg₁₇Al₁₂ broke down and distributed with a streamline shape in magnesium alloy. At the same time, the grain of magnesium alloy refined and dynamic recrystallization occurred. With the increase of deformation, the strength of tubular parts increased, and the hardness was up to 1.036 GPa. The strengthening modes mainly include second phase dispersion strengthening and fine grain strengthening.