Journal of Materials Processing Technology 211 (2011) 1224–1233 Contents lists available at ScienceDirect Journal of Materials Processing Technology journal homepage: www.elsevier.com/locate/jmatprotec Fatigue crack growth behaviour of pulsed current gas tungsten arc, friction stir and laser beam welded AZ31B magnesium alloy joints G. Padmanaban a,∗ , V. Balasubramanian a , G. Madhusudhan Reddy b a Centre for Materials Joining & Research (CEMAJOR), Department of Manufacturing Engineering, Annamalai University, Annamalai Nagar 608002, India b Metal Joining Group, Solidification Technology Division, Defence Metallurgical Research Laboratory (DMRL), Kanchanbag (P.O), Hyderabad 500058, India article info Article history: Received 12 March 2010 Received in revised form 9 February 2011 Accepted 11 February 2011 Available online 18 February 2011 Keywords: Fatigue crack growth Magnesium alloy Welded joints Residual stress abstract The laser beam welded joints offered better resistance against the growing fatigue cracks compared to friction stir welded and pulsed current gas tungsten arc welded AZ31B magnesium alloy joints. The formation of very fine grains in weld region, higher fusion zone hardness, uniformly distributed fine precipitates and favourable residual stress field of the weld region are the main reasons for superior fatigue performance of laser beam welded joints of AZ31B magnesium alloy. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The challenge of significant weight reduction in automobile industry has promoted focus on lightweight metals such as mag- nesium. As a general means of material manufacturing, welding can be used to optimize product design and minimize the costs of production. A detailed account of this is given by Eliezer et al. (1998). Weldability of magnesium alloys has recently been inves- tigated with a variety of processes, particularly gas tungsten arc welding (GTAW), laser beam welding (LBW), laser-GTAW hybrid welding and friction stir welding (FSW). Mustafa Kemal Kulekci (2008) pointed out that, compared to all commercial magnesium alloys; those with aluminum as the primary alloying element are most weldable using any of these three processes. Liu et al. (2006) suggested that, shielding the welding region by inert gas or flux is needed to prevent the fire hazard and risk. Preheating is needed in welding-magnesium applications because of the degree of joint restraint and metal thickness. Schubert et al. (2001) reported that, the laser beam welding (LBW) is a preferred method for joining magnesium alloys because of low heat input, elevated speed and limited deformation. Because laser beam weld- ing (LBW) has been deemed as a high quality and efficiency process, ∗ Corresponding author. Tel.: +91 4144 239734/241147; fax: +91 4144 239734/238275; Mobile: 09443956536. E-mail addresses: gknaban@rediffmail.com (G. Padmanaban), visvabalu@yahoo.com (V. Balasubramanian), gmreddy dmrl@yahoo.co.in (G.M. Reddy). under its action, all kinds of material will be heated to vaporize. The vaporizing pressure presses the molten material ejecting and a small hole (keyhole) is formed in the material being welded and under the focused beam. The keyhole traps the laser beam almost completely. The beam energy is absorbed by the material trough Fresnel absorption of the keyhole wall during multiple reflections of the beam on the wall. Around the keyhole there is a layer of molten material. As the focused beam scans on the material, the keyhole sweeps and the molten material flows around the keyhole from the front to the rare and re-solidified there to form a weld bead. Chang et al. (2006) opined that, recently developed friction stir welding (FSW) is also equally good process for welding magnesium alloys. Problems in fusion welding of magnesium alloys such as solidifica- tion cracking, liquation cracking and porosity are eliminated with friction stir welding due to its solid state nature of process. Signif- icant research is still needed on welding of magnesium alloys to achieve future goals to reduce the vehicle mass and the amount of greenhouse gases. As magnesium is expanding into more critical applications in power train, chassis and body areas, there is a great need for developing wrought magnesium products with improved mechanical properties including fatigue resistance. Most of the available literature are focused on studying the effect of welding processes on tensile properties and microstructure of AZ31B magnesium alloy. Afrin et al. (2008) studied the effect of tool rotational speed and welding speed on microstructure and tensile properties of friction stir welded AZ31B magnesium alloy. Quan et al. (2008) investigated the effect of heat input on microstruc- ture and tensile properties of laser beam welded AZ31B magnesium alloy. Padmanaban et al. (2010) studied the effect of welding pro- 0924-0136/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2011.02.003