Effect of Postweld Heat Treatment on Microstructure, Hardness, and Tensile Properties of Laser-Welded Ti-6Al-4V

Abstract

The effects of postweld heat treatment (PWHT) on 3.2-mm-and 5.1-mm-thick Ti-6Al-4V butt joints welded using a continuous wave (CW) 4-kW Nd:YAG laser welding machine were investigated in terms of microstructural transformations, welding defects, and hardness, as well as global and local tensile properties. Two postweld heat treatments, i.e., stress-relief annealing (SRA) and solution heat treatment followed by aging (STA), were performed and the weld qualities were compared with the as-welded condition. A digital image correlation technique was used to determine the global tensile behavior for the transverse welding samples. The local tensile properties including yield strength and maximum strain were determined, for the first time, for the laser-welded Ti-6Al-4V. The mechanical properties, including hardness and the global and local tensile properties, were correlated to the microstructure and defects in the as-welded, SRA, and STA conditions.

Robotic Nd:YAG Fiber Laser Welding of Ti-6Al-4V Alloy

“…Hardness of the weld metal was determined to be higher than that of the HAZ for both welding speeds. It has been explained by some investigators that the decrease in hardness from weld metal to HAZ was caused by the decreased martensite content and Widmanstatten α structure [30]. When hardness results were examined generally, hardness levels of the HAZ and weld metal were similar.…”

Effect of Microstructure Transformations on Fatigue Properties of Laser Beam Welded Ti‐6Al‐4V Butt Joints Subjected to Postweld Heat Treatment

“…The hardening efect observed in the FZ after SRA1 annealing can be atributed to tempering of the martensitic structure. This efect at relatively low temperatures has already been observed by a number of researchers [6,30,31]. Because metastable ' martensite is supersaturated in stabilizers owing to the difusionless transformation → ', upon annealing, it decomposes into + by precipitation of incoherent particles at dislocations or phase layers at plate boundaries [28].…”

“…A coarse lamellar structure with lower density of defects after annealing at high temperatures has lower strength and higher ductility than martensitic morphology [6,45,46]. This was indirectly conirmed by the decreased microhardness in the FZ after PWHT at high temperatures.…”

“…Kabir et al [6] investigated the efects of stress relief annealing and solution heat treatment followed by ageing on the microstructure, hardness and tensile properties of autogenously welded Ti-6Al-4V but joints. Increased microhardness in the fusion zone after stress relief annealing was observed.…”

Ti6Al4V ALAŞIMININ FİBER LAZER KAYNAK KABİLİYETİ

“…Kaynaklı α+β alaşımlarında düşük süneklik, irileşmiş birincil β oranına ve taneiçi asiküler mikroyapı oluşumuna bağlıdır [24]. 29]. Sertlik sonuçlarına genel olarak bakıldığında, ITAB ve kaynak metali sertlik değerlerinin birbirine yakın olduğu gözlenmiştir.…”