Improvement of surface texture on the hot dip galvanized and galvannealed steel sheets

Abstract

Customers of hot dip galvanized and/or galvannealed steel sheets for automotive are more and more
demanding on high surface quality, paintability and press-formability. The roll texture for temper-rolling in
continuous galvanizing line should be very precisely treated to give a special roughness, which can be
transferred to the Zn-coating surfaces during temper-rolling. Among the various texturing methods, in the
present study, we adopted a newly developed TCT (TopoCrom Texturing) technology and both roll roughness
(high/low Ra) and Cr structures (Open/Closed types) are tested. The products applying TCT had a uniform
and dense roughness pattern and surface characteristics is also compared with the conventionally used EDT
(electron discharge texturing) treatment. It should be noted that TCT technology on commercial galvannealing
coating surface is firstly used and the best condition was Ra=1.2 ?m with closed type; the roughness value
decreases about 35% compared to the conventionally used EDT. On the other hand, in hot-dip galvanized steel
sheets, the best condition was Ra=3.0 ?m with closed type. The friction coefficient was significantly improved
by the effect of the formation of oil pockets on the hot-dip galvanized steel sheet.