MICROSTRUCTURE AND MECHANICAL PROPERTIES OF LASER-WELDED JOINTS OF TI-22AL-25NB/TI-6AL-4V DISSIMILAR TITANIUM ALLOYS

摘要

Laser welding was applied to join 2-mm-thick dissimilar titanium alloys, Ti-22Al-25Nb (at%) and Ti-6Al-4V (wt%). Defect-free joints were obtained. The microstructures and mechanical properties of the welded joints were investigated. The results showed that the fusion zone was mainly consisted of B2 phase and martensite α' phase. The heat affected zone microstructure of Ti-22Al-25Nb and Ti-6Al-4V were different because of different base metal. The heat affected zone of Ti-22Al-25Nb mainly consisted of B2 phase, O phase and α2 phase when the heat affected zone of Ti-6Al-4V mainly consisted of α phase, β phase and martensite α' phase. EDS results showed that the element distribution of each titanium alloy heat affected zone and fusion zone were similar without obvious change. Due to severe agitation, the element distribution was even. Different microstructures in different heat affected zone resulted in an unsymmetrical hardness distribution. The hardness of fusion zone was the lowest of around 300HV when the hardness of Ti-6Al-4V heat affected zone near fusion zone was the highest of around 400HV due to the influence of martensite α' phase. In tensile tests performed at room temperature and 650°C, The tensile strength of the joint reached 1057MPa and 363MPa, respectively. Both theses joints fractured at fusion zone.