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TRODUCTION

LIGHTWEIGHT engineering is usually exploited both in mass production vehicles for fuel saving and in top class ones for enhancing performances.[1–4] The main drivers are product design, high-performance materials, and technological processes.[5–8] During last decade,[9] thanks to the improvement in the structural optimization techniques it is also possible to reduce sections of product design. In the modern automotive industry, thicknesses lower than 3 mm are widely employed for structural assemblies, as chassis or suspensions.[5–7,10–12] The use of lightweight materials could lead to fuel saving and use phase emissions abatement; nevertheless, it is often responsible for increase in the production phase impact, particularly materials processing, thus preventing the expected benefit during use.[4] Aluminum alloys have been widely chosen due to their properties including a high stiffness to weight ratio, low density, good formability, good corrosion resistance, and recycling potential,[11,13,14] which make them the ideal lightweight materials as it allows a mass saving ENRICO BONAZZI and ELENA COLOMBINI, Postdoctoral Fellows, DAVIDE PANARI, Ph.D. Student, ALBERTO VERGNANO, Researcher, and FRANCESCO LEALI and PAOLO VERONESI, Associate Professors, are with the Department of Engineering Enzo Ferrari, University of Modena and Reggio Emilia, Via Pietro Vivarelli 10, 41125, Modena, Italy. Contact e-mail: [email protected] Manuscript submitted May 17, 2016. Article published online October 24, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A

of up to 50 pct over competing materials in most applications.[7,10,15,16] In this background, MIG (Metal Inert Gas) welding, one of the most common joining technologies employed in the automotive industry, despite presenting high productivity and efficiency,[17–22] is affected by some major drawbacks, such as residual stresses and distortions on welded joints.[20,23,24] The high local heating[23] due to the welding torch causes a non-uniform temperature distribution, which is responsible for high thermal gradients across the joint. As a consequence, defects or even early failure of the structures may occur.[18,20] MIG welding of aluminum results is more critical compared to steel, due to the different mechanical and thermal properties of the base and filler metals, which increase the problems of distortion and weld crater size.[24] Hence, the fine tuning of a welding operation in industry usually follows a time- and resources-consuming approach with recursive trials and errors. Instead, the prior estimation of welding deformations would be fundamental to improve product design and process control. As a rule, an experiment is the most realistic method to test a physical phenomenon, even if measurements might introduce errors, or require advanced instruments or, simply, some quantities are unobservable.[19,25–29] Nowadays, numerical simulations, based on finite element (FE) method, have become very useful tools for welding process design, with a plethora of software dedicated