Project
Texturing sheet metal surfaces by selective etching and its influence on functionality of the layered systems

Prof. Carla Vogt
Institut für Anorganische Chemie
University of Hannover, Germany

Cold rolled primary material is used for hot-galvanising. The material is annealed, hot-galvanised and then temper rolled in a continuous annealing line. The microstructure is applied into the sheet metal surface by rough temper rollers. As a negative effect, the temper rolling process causes a slight damage of the zinc layer of fine rolled sheets as well as strain hardening of the material. Due to strain hardening the formability decreases. The goal of this proposal is to reduce the above mentioned disadvantages of mechanical temper rolling by applying etched texture into the sheet metal surface. By a selective etching of the zinc layer a surface with different etching materials microstructure should be generated that is comparable to the surface microstructures generated by temper rolling. The changes in the structure generated by the etching procedures will be characterized by several analytical methods.

Textures on galvanised surfaces can be applied by chemical and electrolytic process. The main task of this project is to find suitable combinations of chemical substances and technical applications to carry out the etching process. Most promising etching substances are H₂SO₄, HCl, NaOH and their mixtures with salts like NH₄NO₃ as well as phosphoric acids. It is possible to generate a great variety of etching rates and structures (micro and macro structures) by altering concentration, mixture ratio and temperature of these materials.

The thickness (5 – 150 μm) and information on layer composition of untreated and etched hot-galvanised layers have to be determined with the non-destructive method of μXRF via the x-ray signals of the elements contained in the layer and in the steel. Therefore the examined materials will be μXRF investigated before and after etching as well as after mechanical treatment in order to explain layer changes (such as changed in structure and thickness). Moreover, comparative flaking tests will be carried out (ICP-OES). Changes in the galvanised layers will be investigated by scanning electron microscopy. Several other analytical methods and testing procedures for the characterization of the induced changes will be applied as well.

The work will be carried out in cooperation with partners from the department of mechanical engineering.