TC4钛合金搅拌摩擦焊接接头组织转变特征

Microstructure Transformation Characteristic of Friction Stir Welded Joint

摘要:

采用搅拌摩擦焊接技术 (friction stir welding, FSW) 分别在空气和强制冷却条件下对TC4钛合金板进行了连接，利用OM和TEM技术研究了焊接接头不同区域的微观组织转变特征。结果表明，FSW接头分为搅拌区、热机械影响区和母材区，各个区域经历了不同的热循环和塑性变形，呈现出不同的微观组织特征。母材区为热轧退火后的初生α和β双相组织。空气条件下，搅拌区为α+β片层结构，组织转变主要为β相转变为片层α+β两相，热机械影响区为等轴晶α和α+β片层的双态组织，组织转变受动态再结晶和相变共同作用。强制冷却条件下，搅拌区为针状马氏体结构，组织转变主要为马氏体相变

Abstract:

TC4 titanium alloy plate was jointed by friction stir welding in air and forced cooling condition separately, and microstructure transformation characteristics in different zones of the joint were investigated by OM and TEM. The result shows that the joint consists of stir zone, thermo-mechanically affected zone and base material, and they have different microstructure characteristics as a result of different thermal cycle and plastic deformation in different zones. Base material annealed after heat rolling is characterized by primary α and β phase. Stir zone is fully lamellar α+β structure, which is mainly controlled by phase transformation from β monophase to lamellar α+β phase in air. Thermo-mechanically affected zone exhibits bimodal microstructure of equiaxed α grain and α+β lamellar microstructure. Its transformation characteristic is dynamic recrystallization and phase transformation. Stir zone is characterized by acicular martensite in forced cooling condition, which is mainly controlled by martensite transformation