Recent R&D status on friction stir welding of Ti and its alloys

Kang, Duck-soo; Lee, Kwang-jin

doi:2015.33.2.1

JWJ > Volume 33(2); 2015 > Article

Special Issue

Journal of Welding and Joining 2015 April;33(2) :1-7.
Published online April 30, 2015.

doi:https://doi.org/10.5781/JWJ.2015.33.2.1

Recent R&D status on friction stir welding of Ti and its alloys

Duck-soo Kang^*, Kwang-jin Lee^*,†

^*Korea Institute of Industrial Technology, Jeonju 561-202, Korea

Correspondence: Kwang-jin Lee Email: kjlee@kitech.re.kr
Published online April 30, 2015

ABSTRACT

This article describes the basic technical concepts for applying the friction stir welding (FSW) process to titanium and its alloys. Titanium and its alloys are demanding applications of FSW. During FSW, a protective atmosphere is needed at the welding region to prevent the joints from oxidation due to the absorption of interstitial elements (O, N, and H) at high temperature. The process parameters for FSW have great influence on the microstructure and properties of the joints. No phase transformation occurred in CP Ti because FSW was achieved below the β-transus temperature. Therefore, the mechanical properties of the joints with CP Ti were governed by recrystallization and grain refinement. Furthermore, the strong crystallographic texture indicating <0001>//ND formed in the stir zone. On the other hands, the phase transformation occurred in Ti-6Al-4V alloy because the process temperature reached above β-transus temperature. For this reason, the mechanical properties of the joints with Ti-6Al-4V alloy were altered by not only recry stallization and grain refinement but also phase transformation during FSW. Engineers who want to get sound FSW joints with Ti-6Al-4V alloy have to pay attention to the control about process conditions.

Keywords: Titanium; Friction stir welding; Mechanical property; Microstructure