International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 04 Issue: 04 | Apr -2017 www.irjet.net p-ISSN: 2395-0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1267 An investigation of the weld current characteristics on twining and tensile strength of the AZ31 alloy sheet joint welded by GTAW Abdulkarim Alzahougi 1 , Bilge Demir 2 , Ahmet Durgutlu 3 1 Technology Faculty, Karabuk University, KARABUK, 1 Technology Faculty, Karabuk University, KARABUK, 2 Technology Faculty, Gazi University, ANKARA ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract - The main focus of this study is to conclude on the twinning of welded joint and the alteration of the tensile properties of the AZ31 magnesium alloy by the processing of the Gas Tungsten Arc Welding with two dissimilar current types, which were alternative and pulsed current, and four altered values of them, Compared to steels, welding of the magnesium alloys may be a very challenging owing to porosity, crack resistance and inter metallic formation and so forth. The technique of metallograph and tensile test were used to assessment the parts of welding joint. The weld microstructure orientation in heat transfer direction was exceptional and equiaxial shaped grain was the prominent grain structure like microstructure of the base metal. Conversely, the grains were bigger in welded metal owing to heat input throughout the welding process. moreover, fusion zone and HAZ of the welded specimens infrequently displayed twin grains. This is the main grain structure kind mainly in pulsed current specimens. It can be determined from the outcomes that the pulsed current is more promising than alternative current for welding of the two mm magnesium alloys sheet with higher accuracy due to the pulsed current cause smaller grains of Alfa-Mg (matrix) and smaller precipitated particle size than alternative current. Key Words: magnesium AZ31 alloy, GTAW, weld current and microstructures. 1. INTRODUCTION: Magnesium alloys were knowledge, to be very significant lightweight metals and numerous academics are focusing on this lightweight structural engineering, The substance has a crest strength of the weight relation and process characteristics. Improvement of structural accessibility of this material strongly counts on the volume of construction as for instance welding procedure performance. The perfect desirability of 1.633 for the solid atomic packing of spheres is as the same as the unalloyed magnesium, which enjoys a hexagonal close-packed (HCP), structure, with a/c ratio of 1.6236. The chief mechanism through which magnesium alloys may be reinforced is precipitation reinforcing, which typically comprises aluminum compounds [1-9]. Many reports concern joint issues of the magnesium alloys [9-15]. On the contrary, there is a little information on accessible works regarding the (GTAW) of magnesium alloys AZ31 utilizing pulsed and alternative current. In addition, high heat generation throughout GTAW is thought to be one reason; however, GTAW can be considered a very useful and laid-back way to connect all metal plates in other methods. GTAW of magnesium alloys has some issues, and the most important of them is the issue of hot cracking [4], however, this issue is seldom stated in works on welding of magnesium alloy AZ31. It can be stated that if the manufacturers offer best conditions for welding magnesium alloys, it will present no problem. Amongst of a general sound techniques for Mg alloys such as the laser beam and electron beam welding techniques. However, as stated previously, these approaches primarily electron beam welding, are not very applicable in terms of preparing the application circumstances. Their significance and benefits come from being high in energy density welding procedures, and hot cracking does not stand severe and attacking difficulties since the little heat input results in comparatively very small alteration and consequently little stresses. Another imperative theme or phenomenon for Mg alloys, mainly comprising Al is Mg–Al intermetallics (IMCs) [1-4]. The formation of Mg–Al IMCs is practically inevitable in Mg and Al welding procedures and features since the morphology of this intermetallics is very operative on mechanical properties. Another topic may be twining for magnesium alloys welding. Barnett [6,7]. Barnett [6] described this for laser beam welding. He cited that the connection between the orientations of twins in HAZ metal is in the orientate of heat transfer. It is not fully obvious in the literature how twinning occurs in weld metal or infusion zone. Though, appreciating this mechanism is very vital as it is well recognized that twinning could be playing a central part in the deformation of hexagonal magnesium[16]. This work concentrates on the parameters of the GTAW welding, which affect the properties of the welded marketable AZ31 magnesium alloy joints and weldability. The AZ31, In addition to the fact that it is a magnesium alloy with decent room-temperature strength, it has so many advantages such as good ductility, corrosion resistance and finally a sensible level of weldability. It is been utilized widely in many applications such as the airplane industry, mobile phones modern technology,