Influence of Form, Surface and Subsurface Areas on the Corrosion Behavior and the Mechanical Properties of Magnesium Alloys

Biermann, D.^{1, a}; Pantke, K.^{1, b}; Denkena, B.^{2, c}; Lucas, A.^{2, d}; Bach, F.-W.^{3, e}; Bormann, D.^{3, f}; Bosse, M.^{3, g}; Hoyer, P.^{3, h}

1)

Institut für Spanende Fertigung, Technische Universität Dortmund, Baroper Str. 301, 44227 Dortmund

2)

Institut für Fertigungstechnik und Werkzeugmaschinen, Leibniz Universität Hannover, 30823 Garbsen

3)

Institut für Werkstoffkunde, Leibniz Universität Hannover, 30823 Garbsen

a) biermann@isf.de; b) pantke@isf.de; c) denkena@ifw.uni-hannover.de; d) lucas@ifw.uni-hannover.de; e) bach@iw.uni-hannover.de; f) bormann@iw.uni-hannover.de; g) bosse@iw.uni-hannover.de; h) hoyer@iw.uni-hannover.de

Kurzfassung

Influence of form, surface and subsurface areas on the corrosion behavior and the mechanical properties of magnesium alloys. The essential aim of the priority program 1168 of the German Research Foundation (DFG) is 'Extending the Range of Applications of Magnesium Alloys'. A part of this program is the presented joint research project. The surface and subsurface properties are significantly influenced by machining processes. Besides the geometry generating finishing processes like turning and milling with limited influence on subsurface properties, the deep rolling process as a non-cutting operation shows major influence. Analyses show that the roughness, hardness, microstructure and residual stresses of AZ31 are modified by the deep rolling process. This results in an improved performance of the magnesium workpieces. Ductile squeezing is a new machining process to close the gap between cutting and rolling processes. Cutting tools with rounded cutting edges and adapted parameters are used to machine magnesium parts below the minimum undeformed chip thickness. Instead of separating the workpiece material the material is squeezed below the cutting edge and therefore ductile compressing the subsurface layer. Subsurface properties similar to deep rolled specimens are achieved with conventional prepared cutting tools. Subsequent to the machining processes the corrosion behavior is analyzed in corrosion tests without and in combination with coatings such as the MagPassCoat. The corrosion properties are examined by means of electrochemical methods (e.g. measurement of current density -potential curves, open circuit potential), in immersion tests and in salt spray tests using aqueous solutions with 0.9% NaCl throughout all studies. For the electrochemical measurements a minicell-system (MCS) which allows measurements on defined surface areas (0.8 square millimeters) is used. The MCS is a miniaturization of the conventional 3-electrode-application with a platinum wire as counter electrode, and a saturated silver/silver-chloride electrode as reference electrode. Based on all the experimental investigations the machining processes, their influence on the surface, subsurface and the resulting corrosion properties are discussed.

Schlüsselwörter

Magnesium, cutting, corrosion, machining, surface

Veröffentlichung

In: Magnesium: 8th International Conference on Magnesium Alloys and their Applications 2009, 26.10.-29.10. 2009, Weimar, Kainer, K. U. (Hrsg.), ISBN 978-3-527-32732-4, S. 1288-1294