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Material Challenges


total vehicle weight by hundreds of pounds in some cases, to help meet the increasingly strict fuel economy requirements. However, welding galvanized steel presents some chal-


lenges. Te zinc coating of the metal can contribute to poros- ity, both on and below the surface of the weld, a quality issue that can require costly rework for manufacturers. Also, with thin materials such as galvanized steel, there is an increased potential of burn-through. Tese challenges oſten can be addressed by using metal-


cored wire that is formulated specifically for use with galva- nized steel. Tis type of wire is capable of providing faster travel speeds at lower temperatures, and it can help improve productivity and efficiency while producing high weld quality, especially when combined with a Pulsed Gas Metal Arc Weld- ing (GMAW) process.


Galvanized Steel Benefits Galvanized steel


has numerous proper- ties that make it a good choice for many automotive manufac- turing applications. It has a protective layer of zinc on its surface, so the material offers excellent corrosion resistance and high strengths, even at thinner gages such as 1.2 mm. Galvanized steel also is more cost- effective than a base metal like aluminum or stainless steel. Because of the CAFE regulations driving the need to


offers cost savings up front compared to electro-galvanized. But it also presents more challenges and can be harder to weld, leading to higher costs in the long run. Electro-galvanized is a more controlled process that results in an even coating of the material—a consistency that makes it easier to weld than hot- dipped galvanized steel.


Galvanized Steel Challenges Surface porosity on galvanized steel is a common issue that


is regulated by American Welding Society (AWS) standards. Te AWS standards only include specifications for porosity on the surface, and they do not address subsurface porosity or zinc-coated steels specifically. Te travel speed used during the welding process directly


As these X-ray images show, certain levels of porosity are acceptable in galvanized steel applications; however, minimizing porosity while also repeatedly maximizing travel speed is key to supporting high quality and productivity.


reduce vehicle weight, these properties offered by galva- nized steel are leading more automotive manufacturers to convert to the material for more applications—typically for components that are thinner than 2 mm and exposed to the external environment, because they need the extra corro- sion resistance. In the past, galvanized steel may have been associated with automotive body skins of less than 1 mm, but in recent years use of the material has expanded into other structural components such as frames, suspension and engine cradles. Tere are different types of galvanized steel, all with their


own characteristics and recommended applications. Te two main types of galvanized coatings used in the automotive industry are hot-dipped and electro-galvanized. Hot-dipped galvanized steel typically is cheaper to produce, and therefore


60 Motorized Vehicle Manufacturing


impacts the presence of porosity. Te faster the travel speed, the faster the weld pool tends to freeze, which can be especially trouble- some since zinc vaporizes at a much lower tem- perature than steel melts. Te tempera- ture dif- ferentiation can lead to gas pockets


becoming trapped because the weld solidifies before the zinc gas can escape. Te ability to minimize porosity while also maximizing


travel speed is key to supporting high quality and productiv- ity in automotive manufacturing applications using galva- nized steel. In addition to porosity, other potential challenges when


welding galvanized steel include increased risk of burn- through due to the heat input, and the presence of silica islands in the weld, especially those that may break free aſter the e-coat or paint process or those that adhere to the toes of the weld, which can be a potential source of rust later on in the life of the part. Another issue for manufacturers to consider when con-


verting to galvanized steel is the weld fume created during the process. Even though most automotive applications


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