One-sided laser beam welding of autogenous T-joints for 6013-T4 aluminium alloy A.C. Oliveira a,b,⇑ , R.H.M. Siqueira a,b , R. Riva b , M.S.F. Lima b a Instituto Tecnológico de Aeronáutica, ITA, Pça.Mal.Eduardo Gomes, 50, São José dos Campos, SP 1228-900, Brazil b Instituto de Estudos Avançados, IEAv-DCTA, Trevo Cel.Av.José.A.A.do Amarante, 1, São José dos Campos, SP 12228-001, Brazil article info Article history: Received 25 July 2014 Accepted 20 September 2014 Available online 6 October 2014 Keywords: Laser beam welding Yb-fiber laser Autogenous T-joints Aluminium alloy abstract Autogenous T-joints for aluminium skin-stringer component performed by one-sided laser beam welding process was conducted using a high power Yb-fiber laser. The influence of the shielding gas, seam angle, beam focal position, and beam positioning relative to weld centerline were investigated regarding to weld microstructural features. The joint mechanical behavior was evaluated concerning to the sheet roll- ing directions. It was observed that a precise control of the process parameters enabled to obtain weld beads with acceptable dimensional and geometric characteristics and minimizing weld defects. Helium shielding gas produced higher aspect ratio welds than those with pure argon. Although, pores were observed in the fusion zone, they represented only about 5% of the weld bead area. The optimal beam positioning should remain up to 0.2 mm relative to junction line, for seam angles between 10° and 15°. The weld mechanical behavior depended on the sheet rolling direction. Joint efficiency up to 85% were obtained after hoop tensile tests when the weld bead longitudinal-section was perpendicular to skin rolling direction and parallel to the stringer rolling direction. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Laser beam welding has been studied, and even employed in the aeronautical industry, particularly for the joining of skin-stringer fuselage sections [1,2]. The traditional riveting joining method, although highly automatized, offers a small potential to increasing production rate or aircraft weight savings [2,3]. Some studies have demonstrated the laser joining technique as a possible replacement of riveting [4,5]. Usually a filler material has been used during laser welding to fill the gap existing at the joint or improves the weld bead toughness [6]. Braun [7,8] analyzed the influence of the filler wire composition on the weld- ing process stability. He proposed a filler wire containing large amounts of silicon for adjusting weld pool chemistry of the AA6000 alloys, ensuring the elimination of solidification cracks in the fusion zone. Squillace and Prisco [9] also investigated the influ- ence of filler additions on micro and macro-mechanical behavior of T-welded joints. Their results suggested the possibility to reduce the weakening at the heat affected zone of aluminium alloy welds using a filler wire with high melting latent heat. However, laser welding with filler wire has been considered an additional difficult for industrial application, having many parameters and stringent requirements for wire positioning [10]. According to Tao et al. [11], the feeding position, wire feeding direction, and wire feeding angle had significant influence on the laser welding process stabil- ity and on pore formation. Therefore, the use of filler wire can limit the utilization of laser technology to joint skin-stringer compo- nents, since the process parameters are quite complex and defect generation must be strictly controlled. Laser beam autogenous weld under T-joint configuration could be much simpler by minimizing the difficulties of the introduction of filler metal. One of drawbacks for the autogenous laser welding is the presence of air gaps existing at the joint region, which can promote defects such as concavity, sidewall fusion defects, root suck-up, and weld undercuts [10]. According to Salminen [6], in the typical butt joint, the widest acceptable gap for autogenous laser welding is usually 10% of the material thickness. Dawes [12] concludes that a gap width of 0.14 mm in sheet thickness of 2 mm leads to concavity defect, reducing loading to 86%. Yang et al. [13] showed that, in the double-sided laser beam welding, parameters such as: incident beam position, beam angle, and beam separation distance affect strongly the metallurgical quality of the T-joints. Prisco et al. [14] showed that the distribu- tion of weld bead along of skin-stringer components influences http://dx.doi.org/10.1016/j.matdes.2014.09.055 0261-3069/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Universidade Federal de São Paulo, UNIFESP, Rua Talim, 330, São José dos Campos, SP 12230-280, Brazil. Tel.: +55 12 3309 9600, +55 12 981447036. E-mail addresses: aline.capella@unifesp.br, alinecapella@gmail.com (A.C. Oliveira). Materials and Design 65 (2015) 726–736 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes