1st Paragraph: The trends in automotive manufacturing over the past 40 years have been toward the use of lighter-weight materials to manufacture vehicles with improved fuel economy. Replacing traditional steels with advanced high strength steel (AHSS) with a reduced thickness is one approach to decreasing the weight in chassis applications. With the reduced thickness, however, come concerns about corrosion resistance. One solution to the corrosion problem is to use a zinc (Zn) coating in concert with e-coating for chassis applications. Utilizing Zn for these applications does present a joining concern, however. Because the boiling point of zinc is lower than the melting point of steel, as the base material is heated to its melting point, the zinc coating vaporizes, which leads to porosity. One way to reduce the porosity is to reduce the travel speed, which gives the zinc vapor more time to escape before the molten steel solidifies. As the travel speed is reduced, however, the chances of burn-through increase, making it very difficult to produce a sound weld.
Author: Susan R. Fiore