Microstructure and texture distribution of Ti–6Al–4V alloy joints friction stir welded below β-transus temperature

Abstract

Ti-6Al-4V alloy plates with a thickness of 5 mm were successfully joined by friction stir welding (FSW) at a significantly lower than the β-transus temperature, and the microstructure and texture evolution in the stir zone (SZ) along the thickness and transverse directions of the joint were clarified. The fully equiaxed α structure was observed even near the top surface in the 50 rpm joint, while a mixture of the lamellar structure with equiaxed α grains was found near the top surface in the 150 rpm joint. The existence of the lamellar structure resulted in a strong [0001]α concentration in this area due to the variant selection during the phase transformation. A bimodal structure was formed in the retreating side (RS) of the SZ obtained at 50 rpm, and a higher area fraction of the coarse grain structure was found in the RS of the SZ center than in the RS located 0.1 mm from the top surface due to the gradients in the strain, strain rate and temperature. The local texture measured by EBSD clarified that [0001]α was perpendicular to the welding direction on the advancing side (AS), and gradually rotated toward to the welding direction when the measurement positions were moved to the RS in the SZ of the Ti alloy joints. The difference in the distribution of the [0001]α concentration direction in

An Overview of the Thermomechanical Processing of α/β Titanium Alloys: Current Status and Future Research Opportunities

“…The specific microstructure is as a function of starting structure (e.g., fully equiaxed, duplex, or fully lamellar) and the local strain, strain rate, and temperature (sub-or supertransus) experienced during the joining operation. [253][254][255][256][257][258] Local strains and strain rates in the stir region have been estimated via numerical modeling to reach as high as 100 and 1000 s À1 , respectively. For preform structures that are fully-equiaxed (mill-annealed) or duplex (equiaxed-a particles + secondary-a platelets), regions that remain below the transus usually exhibit a mixture of a particles (with a grain sizes of the order of 1 to 3 lm) and colonies of secondary a.…”

Linear Friction Stir Welding of Medium Carbon Steel at Low Temperature

“…Recently, many studies have been conducted on the solid-state joining processes in which the welding can be performed at a low temperature, so that the transformation to martensite that occurs during cooling can be suppressed to avoid embrittlement of the joint. [2][3][4] Linear Friction Welding (LFW) is one of the solid-state joining processes, in which a joint is obtained through the relative motion of two components under a high contact…”

Corrosion properties of low carbon steel prepared by submerged friction stir processing

“…Nowadays, FSP has been applied to low‐melting metals, such as aluminum and magnesium alloys . In recent years, FSP has also been successfully applied to high‐melting metals, such as titanium alloys, copper alloys, and steels . Compared with other SPD techniques, FSP can prepare the equiaxed dynamically recrystallized grains with a large fraction of high angle grain boundaries.…”