Page 52 - MetalForming September 2013

Metal-Cored Wire
for Welding Galvanized Steel Full Speed Ahead
Galvanized steel’s most positive attributes also make the material challenging to weld. Run metal-cored wire in place of solid wire to minimize the likelihood of burnthrough and weld porosity, without slowing down.
BY KEVIN PAGANO AND DERYCK HART
Due to the protective layer of zinc oxide on its surface, galvanized steel offers excellent corrosion resistance as well as high strength, even at thinner gauges. However, these same properties also challenge metalformers required to weld galvanized steel. For example, thinness increases the likeli- hood of burnthrough, while the zinc- oxide coating can cause weld defects when improper welding procedures are used.
Many automotive suppliers use gal- vanized steel in the 1.6- to 4-mm range, for components such as frames, engine cradles and suspension links, and use even thinner material for other areas of
Kevin Pagano is segment engineering manager, Miller Electric Mfg. Co.; 920/734-9821, www.millerwelds.com. Deryck Hart is director, automotive seg- ment North America, Hobart Brothers Co.; 937/332-4000, www.hobartbroth- ers.com.
the vehicle. In fact, it’s not uncommon to find autobody skins on galvanized steel as thin as 0.7 mm.
Most automotive manufacturers use one of three types of galvanized steel: hot-dipped, galvanealled or electrogal- vanized. Of these, hot-dipped galvanized steels tend to be the most challenging to weld, but also the most prevalent in the industry due to their lower cost.
Hot-dipped material tends to have an uneven surface thickness that makes the completion of consistent welds
particularly challenging. To obtain its zinc-oxide finish, the material passes through molten zinc at high tempera- tures (in excess of 800 F), after which the zinc undergoes a series of chemical reactions. The result is the tough zinc- oxide surface that provides a protective barrier and acts as a sacrificial anode to provide corrosion resistance.
Welding Challenges
Most automotive manufacturers weld galvanized steel with the gas-
50 MetalForming/September 2013
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Fig. 1—Penetration profile of a weld created with metal-cored wire and pulsed GMAW, optimized for galvanized steel.