Influence of Die Lubricants on Pickling and Conversion Treatment of High-Pressure Die-Cast AM30 Magnesium Alloy

The pre-treatment of magnesium-based components plays an important role in surface engineering technology to guarantee good adhesion of the final coating system to the magnesium substrate in order to achieve good corrosion resistance. This paper focuses on the influence of two different die lubricantsone based on mineral oil, the other on siloxaneon the pickling and conversion treatment of an AM30 alloy. The surface conditions after casting, pickling, and conversion treatment were determined by X-ray-induced photoelectron spectroscopy, spark erosion, optical emission spectroscopy, IR spectroscopy, and scanning electron microscopy (including EDX). The influence of the different die lubricants on the result of the pickling treatment in terms of surface morphology and composition was significant. The mineraloil-based lubricant was found to be removed more easily and uniformly from the surface. Only sufficient removal of the die lubricants can guarantee homogeneous and uniform formation of the conversion coating.