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Microstructural Characterization of Dissimilar Joint: SAE1008-2340 Welded by GMAW Process L. L. Rodríguez López, G.Y. Perez-Medina, L.A. Carrasco González, R.J. Praga Alejo and F.A. Reyes-Valdés. Corporación Mexicana de Investigación en Materiales, Saltillo, Coahuila, México. Email: [email protected] ABSTRACT Gas metal arc welding (GMAW) of a sub-frame automotive industry was studied, applying a design of experiment (DOE) in Minitab and Matlab software. Voltages, welding speed and wire feed speed was defined as input variables; legs and throats of welding were output variables in millimeters dimension. The requirement for GMAW process was to achieve complete penetration, minimum values acceptable of legs and throat indicated in AWS D8.8M:2007 “Specification for automotive weld quality-arc welding” without any discontinuity, like undercutting or porosity. The required of quality were difficult to achieve due to the materials have microstructural and mechanical properties different, the SAE 1008 has 279MPa for ultimate tensile strength (UTS) and the microstructure consist of ferrite matrix with some small areas of cementite, while SAE 2340 has 456MPa of UTS with a combination of perlite and ferrite. It was possible obtain good quality welds with proper geometry and defect free with help to design of experiment. The conditions needed were a combination of parameters to not obtained significant change microestructural characterized by optical microscopy, stereoscopy and scanning electron microscopy. Keywords: GMAW, Microstructure, SEM.

INTRODUCTION The new competition for good quality products in the automotive sector requires making improvements and implementations in industrial processes for the product to be accepted in a competitive market. Different materials in an automobile vehicle are subject to different working conditions such as weight reduction with impact resistance, therefore, has increased the use of high strength steels in the automotive industry, such as steel SAE 2340 [1,2]. These materials are joined by welding, since the bonding method is the most important in this type of industry. In this way we will be able to identify these changes, mechanical properties, behavior and predict potential failures of these materials. The welding process gas metal arc welding (GMAW) is a method widely used in the automotive sector, which is always in implementation of improvements in process parameters. GMAW welding is a process that uses an arc between a continuous electrode filler metal and the weld pool. The process is performed under a shield gas externally supplied without application of pressure [3, 4]. Therefore, the metallographic characterization and microhardness analysis are very important for the effect on the properties due to phase transformations that may occur in this type of material, when subjected to a welding process [5,6].

EXPERIMENT PROCEDURE The materials used in the sub-frame automotive are SAE 1008 and SAE 2340 with 1.5mm and 2.7mm thickness, respectively. The configuration of the jo