International Journal of Engineering and Technical Research (IJETR) ISSN: 2321-0869, Volume-2, Issue-12, December 2014 43 www.erpublication.org Abstract— Geometry, microstructure, mechanical and corrosion properties of the Nd-YAG laser welded Ti-6Al-4V alloy were studied and compared with those of the GTA butt welded joints. The results showed that the laser welding parameters played an important role in obtaining satisfactory joint quality. The extent of surface discoloration which is an indicator of atmospheric contamination was influenced mainly by flow rate of the shielding gas rather than its type or pre-weld cleaning technique. Laser square butt weld profile was significantly improved by shifting the focal point up to 2mm below the specimen surface. Autogeneous full penetration laser welded butt joints could be produced using a welding speed of up to 5m/min. In comparison with the GTA welding, the laser welding with its lower heat input resulted in a pronounced decrease in the distortion level as well as significant decrease in the fusion zone size. On the other hand, the laser welded specimens had higher hardness of the fusion zone. As a result, inferior impact and corrosion properties were expected. However, opposite results were obtained where the laser welded joint demonstrated better impact and corrosion properties. The results showed that the properties of the welded joints were influenced not only by the fusion zone microstructure but also by the fusion zone size. Index Terms— Ti-6Al-4V alloy, Nd-YAG laser welding, Fusion zone size, Mechanical properties, Corrosion resistance. I. INTRODUCTION Since the introduction of titanium and its alloys in the early 1950s, they have been widely used in the aerospace, energy, and chemical industries. The combination of high strength to weight ratio, excellent corrosion resistance and mechanical properties makes titanium the best material for many important applications [1]-[3]. Today, titanium alloys are used for demanding applications such as the static and rotating gas turbine engine components. Some of the most critical civilian and military airframe parts are made of these alloys. The use of titanium has expanded to include applications in nuclear power plants, food processing plants, oil refinery heat exchangers, marine components and medical prostheses. Ti-6Al-4V is the most widely used titanium alloy and it accounts for about 70% of all Ti-alloys produced. It is a two phase α+β titanium alloy with aluminum as the alpha stabilizer and vanadium as the beta stabilizer. This Manuscript received November 03, 2014. Abdel-Monem El-Batahgy, Central Metallurgical R&D Institute, Cairo, Egypt, +20 122 4608265 Tarasankar DebRoy, Pennsylvania State University, Pennsylvania, USA, +1 814 865 1974 . high-strength alloy can be used at cryogenic temperatures and at high temperatures up to about 800°F (427°C). It is used in the aerospace, marine, power generation and offshore industries and as implant materials in the medical and dental fields [4]-[6]. Welding offers an efficient and cost-effective means of fabricating structural assemblies containing this alloy. Understanding how the mechanical and corrosion properties of the Ti-6Al-4V alloy joints are affected by the welding variables are important for their serviceability. Structures made of this titanium alloy are fabricated using mainly conventional fusion welding processes including gas tungsten arc (GTA) welding process [7]-[12]. However, titanium alloys are noted for being difficult to weld by conventional fusion welding. Recently, new techniques have been considered to achieve reliable welds with minimum distortion for the fabrication of components of both conventional and non-conventional materials. Of these techniques, laser welding [13]-[15] that can provide a significant benefit for the welding of titanium alloys because of its precision and rapid processing capability. There is an increasing interest on the laser beam welding of Ti-6Al-4V alloy and good success has been reported [16]-[20]. However, little has been published about the weldability of this alloy using high power solid-state Nd:YAG laser [21]-[23]. Previous investigations have demonstrated that the rapid solidification and quench associated with laser welding affects the microstructure and properties of the welded joints [24]. In other words, the microstructure of both the weld metal and heat affected zone of Ti-6Al-4V alloy is affected by the cooling rate from the peak temperature as a function of heat input. Consequently, it is expected that the microstructure of fusion zone then, the mechanical and corrosion properties of welded joints are affected by type of the welding process. However, this research area is far from complete and more works are required for the successful selection of the efficient and cost-effective welding process for fabricating large structures of titanium alloys. The present study has been concerned with improved understanding of the weldability of Ti-6Al-4V alloy using a 4kW Nd-YAG laser beam in comparison with the conventional GTA welding process. The effect of laser beam welding process on size and microstructure of fusion zone then, on mechanical and corrosion properties of Ti-6Al-4V alloy was examined. The effects of pre-weld cleaning technique, shielding condition, welding speed and focused beam position on the joints quality were investigated. Moreover, the mechanical and corrosion properties of the laser beam welded joints were compared with those of the GTA welded joints. Nd-YAG Laser Beam and GTA Welding of Ti-6Al-4V Alloy Abdel-Monem El-Batahgy, Tarasankar DebRoy