The next change with respect to zinc coating steel technology relates to the perennial problem of pick-up of zinc particles/build-up of zinc on press tools, and accelerated electrode tip wear due to alloying of molten zinc with the copper-rich spot welding electrodes. These aspects must be addressed if efficiency of all links of the process chain are to be improved. In a recent BRITE-EURAM collaborative project6 it has
been demonstrated that using physical vapour deposition techniques coatings as low as 4–5 microns can be deposited which give advantages with respect to both press performance and electrode tip life. Although presenting a challenge in terms of the production of strip wide enough for automotive production this has already been shown as a viable alternative method of zinc deposition in Japan7 and the economics approach those of the electrogalvanizing process. The advantage of the process as proven in the joint European project was that alloyed layers of zinc plus elements such as Ti, Cr and manganese could be deposited which proved to show enhanced corrosion resistance compared with standard automotive quality zinc coated steel.
The direction of this work must now be redirected to optimize preferred alloying elements, the format of sandwich layers, and regarding the processing parameters such as the nature of the vapour itself. Initial indications show that this unique method of alloying could eventually lead to a product which answers all the questions posed – cost, coating integrity, corrosion resistance and processability.
Materials for Automobile Bodies
Geoff Davies F.I.M., M.Sc. (Oxon)
AMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK OXFORD
PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO
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1 comments:
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