Effect of Postweld Heat Treatment on Microstructure, Hardness, and Tensile Properties of Laser-Welded Ti-6Al-4V
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INTRODUCTION
FOR structural applications, the utilization of titanium alloys has several benefits over steel and aluminum alloys. Specifically, the combination of low density, good tensile properties (up to a temperature of 873 K [600 C]), good corrosion resistance, and chemical compatibility with, for example, carbon fiber-reinforced composite renders a high attraction for applications especially in aerospace.[1,2] Of the various titanium grades, the most popular is Ti-6Al-4V, an a + b alloy that contains 6 wt pct Al to stabilize the HCP a-phase and 4 wt pct V to stabilize the body-centered cubic b-phase at room temperature. Of importance for increasing the application of titanium alloys is the development of cost-effective joining processes that render high mechanical performance of the structural assembly. For fusion welding processes, titanium exhibits some excellent characteristics such as good fluidity of the molten metal and low thermal conductivity.[3] However, the high reactivity of titanium with atmospheric gases at temperatures above 673 K (400 C) and especially in the liquid state[4] has traditionally led to the utilization of high-vacuum electron beam ABU SYED H. KABIR, formerly Master Graduate Student, Concordia University, Montre´al, Que´bec H3G 1M8, Canada, is now Ph.D. Candidate, McGill University, Montre´al, Que´bec H3A 0C5, Canada. XINJIN CAO, JAVAD GHOLIPOUR, and PRITI WANJARA, Research Officers, are with the Aerospace Manufacturing Technology Center, Institute of Aerospace Research, National Research Council Canada, Montre´al, Que´bec H3T 2B2, Canada. Contact e-mail: [email protected] JONATHAN CUDDY and ANAND BIRUR, Senior Engineers, are with the StandardAero Limited, Winnipeg, Manitoba R3H 1A1, Canada. MAMOUN MEDRAJ, Professor, is with the Department of Mechanical and Industrial Engineering, Concordia University. Manuscript submitted October 20, 2011. Article published online June 3, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
welding for component assembly, particularly for the aerospace industry. Recent advancements in high-power laser technology have resulted in the ability to use lasers for the manufacturing, repair, and overhaul of titanium alloys for aircraft structures and aero engine components. With adequate shielding gas protection, titanium alloys can be laser welded and the joints can be similar in quality and performance to the electron beam welds. Particularly, the high energy density of laser welding allows low heat input and fast welding speeds (high productivity) that can produce a high aspect ratio weld (penetration depth/bead width) with a narrow heat-affected zone (HAZ), low distortion, and high weld quality including refined prior-b grain size. In addition, laser welding of titanium alloys with local shielding gas protection offers manufacturing flexibility as well as ease of automation.[5–7] Of the various titanium grades, Ti-6Al-4V has been reported to have good weldability, but its strength, ductility, and toughness may be significantly varied, depending on the ther
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