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For the last few years zinc magnesium alloys on cold rolled steel were investigated in detail because of their potential to provide better corrosion protection than pure zinc coatings [1]. However [2,3], especially in the construction industry. This is mainly due to improved corrosion performance when compared to classical hot dip galvanized steel [4,5], which permits a reduction in coating thickness in some applications. The automotive industry has also become more interested in the new material, mainly because of advantages in corrosion performance, but also because of material test results that indicate the advantages of tribology and tool wear. Hot dip galvanized zinc magnesium coatings (HDG/ZM) do not consist of a single phase throughout the coating thickness but show a complex composition [6] of different phases (see Fig. 1). Also the hardness of the coating is affected by adding magnesium. While hardness of a classical zinc coating is about 70-90 HV0.02, the hardness of HDG/ZM (2%Al and 2%Mg) is in a range of 130-160HV0.02. All these differences to classical hot dip galvanized zinc coatings (HDG/Z) have an influence on the processing properties of the new material, among them tribology and tool wear. Tribological and tool wear tests have to be conducted prior to introducing the new material to the automotive industry. Some of these studies, at least with respect to model parts, are presented and discussed in this paper.

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In the sheet metal forming industry, tools are subject to mechanical, thermal, chemical and tribological loads. One of the major problems in forming operations of hot-dip galvanized sheet metal is galling (build-up of zinc flakes on the tool). This phenomenon develops gradually as an adhesion on the tool surface. The adhesive wear leads to high rejection and reworking costs for large car body forming tools. Due to economic aspects and the easy castability, the forming tools are made of cast iron. These materials tend to high adhesive wear. The aim of this project is to find a three-dimensional surface parameter, which describes a tribologically advantageous surface of forming tools in order to reduce galling. An additional objective is to optimize tool materials, heat treatment and surface coating. The evaluation of galling under laboratory conditions is based on strip drawing tests. The characterization of tool materials was executed for grey cast iron (EN-GJL-200/250) and nodular cast iron (EN-GJS-700). Investigations demonstrate that the processing methods and test parameters like sliding speed and temperature have a significant influence on galling. Three-dimensional surface parameters have also shown an effect on galling.

Strength Steels) have received growing attention in the construction of light-weight car bodies with excellent crash-performance. With the rising strength of these materials, the requirements for forming and cutting tools are also increasing permanently. To investigate the tool performance for such conditions, four different cold work tool steels (1.2379 -Sverker21, Sleipner, 1.2358 -Carmo and Caldie), one of them (1.2379 -Sverker21) additionally PVD-coated, were used in their typical heat treatment condition to compare the wear behavior and the cutting performance. The tests were performed on semi-industrial forming and cutting press under industrial process parameters on partially preformed test pieces of the steel CP1000. The measurement methods applied include optical as well as tactile measurement methods to measure the tool wear, optical methods to investigate the cutting zone and the burr formation at the workpiece as well as scanning electron-microscopy to characterize the tool surface regarding wear, fracture and adhesion of the zinc coating. Except for the lower alloyed surface hardened and nitride tool steel (1.2358 -Carmo), which showed early failure, all other tooling solutions easily reached 100,000 test pieces with good workpiece quality. Nevertheless, small partial fracturing at the cutting edge was found at all tools. Best results regarding wear, but especially lowest zinc adhesion were found at the PVD-coated tools.