Effect of Heat Treatment on Microstructure and Tensile Property of Ti-6Al-6V-2Sn Alloy

Qirui Wang,Ming Hu,Xiaofei Lei,Limin Dong,Rui Yang,Xin Xu

doi:10.3390/met11040556

Abstract

The microstructure and tensile properties of Ti-6Al-6V-2Sn alloy heat-treated at different solution and aging temperatures has been systematically investigated. Specimens were solution-treated at 970 °C (above the β transus) and 920 °C (below the β transus), respectively, followed by water quenching. When the alloy is quenched from 970 °C, α’ (hcp) and α˝ (orthorhombic) martensite phases co-exist in the microstructure. When it is quenched from 920 °C, α´ martensite phase does not form, while equiaxial primary α (αp) phase and α˝ are found in the microstructure. The results also show that the strength of the alloy increases but the ductility deteriorates as the solution temperature becomes higher when the aging treatment is unchanged. This is because the volume fraction of equiaxial αp phase is lower but the volume fraction of the acicular secondary α (αs) phase is higher for higher solution temperature. When the alloy is aged at different temperatures after the solution treatment at 900 °C, the strength of the alloy decreases with the increase of aging temperature and the ductility shows the opposite trend as the size of the acicular αs becomes longer and its volume fraction is lower at higher aging temperature.

Highlights

IntroductionTwo-phase α + β titanium alloys have been commonly used in aerospace, automotive, energy, biomedical, and other industries due to its high specific strength, excellent fatigue, and corrosion resistance [1,2]
Their X-ray diffraction (XRD) patterns show that they are composed of α and β phases. These experimental results indicate that the Ti-6Al-6V-2Sn alloy structure is composed of α and β phases after solution and aging heat treatments
For solution-treated and quenched Ti-6Al-6V-2Sn alloy, the phases formed after quenching are closely related to the solution temperature and the composition of β phase

Summary

Introduction

Two-phase α + β titanium alloys have been commonly used in aerospace, automotive, energy, biomedical, and other industries due to its high specific strength, excellent fatigue, and corrosion resistance [1,2]. Ti-6Al-6V-2Sn alloy, as one of typical two-phase titanium alloy, developed from Ti-6Al-4V has very good comprehensive performance and machinability, which is used for aircraft fuselage, rocket engine parts, and aerospace fasteners [3,4]. Compared to Ti-6Al-4V, Ti-6Al-6V-2Sn has more β stable elements with better hardenability and higher application temperature. Similar to Ti-6Al-4V, it shows a good response to heat treatment [5,6]. Bimodal microstructure usually endows α + β Ti alloys with good mechanical properties, which is vital for the application of the alloys [7]

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