A comparative study of fatigue behaviour of MAG and laser welded components using reliability analysis Marco Dourado a,n , Delfim Soares a , Joaquim Barbosa a , António Marques Pinho a , José Meireles a , Paula Branco b , Carlos Ribeiro c , Carlos Rei c a Mechanical Engineering Department, Azurém Campus, 4800-058 Guimarães, Portugal b Instituto de Soldadura e Qualidade, Rua do Mirante, no. 258, 4415-491 Grijó, VNG, Portugal c Sodecia Centro Tecnológico S.A, Rua Engenheiro Frederico Ulrich, 2650, 4470-605 Maia, Portugal article info Article history: Received 19 January 2014 Received in revised form 18 March 2014 Accepted 20 March 2014 Available online 27 March 2014 Keywords: Fatigue Reliability analysis Weld joint MIG/MAG Laser welding abstract Fatigue is one of the main causes of failure of structures and mechanical components, occurring due to the progressive weakening of their strength that reduces significantly their lifetime, when subjected to cyclic stresses over time. In welded components, the joints are the zones most susceptible to crack by fatigue. Therefore, the base of this study are the Metal Inert Gas/Metal Active Gas (MIG/MAG) and LASER welding manufacturing processes, focused in three main areas involved in an automotive metallic system under dynamic loads: Fatigue testing in order to prevent structural collapse; Heat Affected Zones (HAZ) characterization to evaluate the material properties modification originated by those different technologies; Reliability analysis in order to analyse the performance of the samples and to select the best connection in terms of product life cycle. For this purpose, samples representative of industrial automotive applications (long welds) have been selected to carry out this work. Two types of connected specimens were manufactured, consisting of two steel plates of different thicknesses, overlapping and welded by the MAG process (type A) or the Laser process (type B). Metallographic characterization was performed for both typologies, namely macrostructural and microstructural characterization of the weld joint, and respective HAZ. Mechanical properties were inferred by measuring and mapping microhard- ness variation on the neighbour of the weld joint. Fatigue tests were carried out for specimens type A and type B, using 15 samples of each type that were tested under 3 levels of stress amplitude. The samples manufactured by the Laser process show better fatigue behaviour when compared to the samples manufactured by MAG welding. The better weld joint solution is proposed in accordance with the reliability analysis of the obtained fatigue test results. & 2014 Elsevier B.V. All rights reserved. 1. Introduction The industry, including automotive, struggles continuously with the need to increase competitiveness and profitability. Due to their structural importance, metallic components and systems represent the major part of the weight of an automobile. These metal components are connected together in order to create multiple subsets, to get the final product. Therefore, several sets of metallic components/systems need to connect together. Due to specific structural needs, the dynamic requests change all over the metallic components/systems. In addition, the continuous search for lighter and more resistant solutions, with lower costs and reaching the dynamic specifications and quality, with a perfect repeatability of the manufacturing process, force the designers to continuously search for solutions in order to optimize this set of variables. Furthermore, if the metallic components/systems have to respect security's characteristics or are exposed to continuous envir- onmental and mechanic attacks, they will require increased attention. Welding is the most used technological process to connect two components and MAG/MIG, TIG, Submerged Arc and Laser processes are those more commonly used in industrial applications. It is known that the welded joint of two components is the most susceptible zone to initiate fatigue crack, reducing signifi- cantly the component lifetime [1]. Fatigue is the result of regular or irregular cyclic stresses imposed on the component, that may lead to fatigue cracks, Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/msea Materials Science & Engineering A http://dx.doi.org/10.1016/j.msea.2014.03.067 0921-5093/& 2014 Elsevier B.V. All rights reserved. n Corresponding author. E-mail addresses: mdourado@dem.uminho.pt (M. Dourado), dsoares@dem.uminho.pt (D. Soares), kim@dem.uminho.pt (J. Barbosa), acmpinho@dem.uminho.pt (A. Marques Pinho), meireles@dem.uminho.pt (J. Meireles), pabranco@isq.pt (P. Branco), carlos.ribeiro@ct.sodecia.com (C. Ribeiro), carlos.rei@ct.sodecia.com (C. Rei). Materials Science & Engineering A 606 (2014) 31–39