Properties of MIG Brased Joints of Thin Sheets

2007

For several years, automotive indu stry is seeking for new processes to replace MIG welding in joining thin zinc coated plates [1,2]. In the last ten years, special attention was paid to the MIG Brazing process (MIGB), which became an optimum solution for this industrial application [3-6). MIGB was found to be the most affordable joining technique to replace arc welding of thin Zn coated plates, due to some obvious advantages, namely reduction of the Zn burn-off during brazing, lower residual stresses and geometrical distortions. Despite the lower melting temperature of the filler alloys the effects of the electric arc heat input of the MIGB process, especially on the zinc layer integrity and on the physical chemical and metallurgical properties of the joint, have been found possible to be deleterious. The present research was meant to respond to the needs of the controlled transfer of the molten metal through the electric arc directed to high quality requests / applications, after identifying MIGB for automotive applications, to join thin (0.8+1.00mm) Zn coated plates, with Cu based electrode wire [1-3]. This paper addresses the influence of MIGB parameters on process stability, as well as the mechanical, corrosion and metallurgical properties of0.8mm galvanized thin sheet joints for automotive industry when using different gas mixtures. The features of an optimum MIGB procedure are still under debate, since the optimisation criteria may vary, according to the needs of each specific technological application [5]. Lower Heat Input (HI) requiring lower values for the intensity of the welding mean current and leading to the controlled short-circuit transfer mode, with the main disadvantages of less spatter, wetting and inappropriate seam shape, may define one type of approach. Good wetting properties, with good looking bead, but controlled pulsed arc obtained for higher values of current and HI, with more vaporised zinc, wider Heat Affected Zones (HAZ), partially destroyed zinc layer and with more unacceptable defects may describe another approach. Besides these practical targeted procedures, several fundamental aspects arouse. Due to its basic importance, but also to the practical implications, the metal transfer through the electric arc is by far the most relevant and permanently envisaged, on the approach used to define the limits of experimental procedures characterised by lower heat inputs [7, 8]. Due to the actual demand of a wider use of MIGB invarious manufacturing processes, the research undertaken aimed at contributing to optimise the MIGB procedures, targeting mainly the minimisation of the heat input, assuring all the quality indicators of the joint.

Authors in the community:

• 

  M

  Maria Luisa Coutinho Gomes de Almeida

  ist11722

  Affiliations and sources

  IST > LAETA

  Laboratório Associado de Energia, Transportes e Aeronáutica

  IST > IDMEC

  Instituto de Engenharia Mecânica

  IST > DEM

  Departamento de Engenharia Mecânica

Welding and Materials Testing

14

25

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mechanical-engineering - Mechanical engineering

eng - English