Abstract.Investigations of AZ91D revealed a strong influence of mainly the following microstructural parameters on corrosion: porosity, the eutectic, the Al-content of the Mg-phase as well as the volume fraction and distribution of gamma-Al 12 Mg 17 . Further an improved corrosion resistance was observed by the addition of rare earth elements. The influence of Ce on microstructure and corrosion of sand cast and high pressure die cast AZ91D with 0.5-2.0 wt.% Ce was investigated by SEM before and after potentiodynamic polarization measurements in pH7.5 (bi-distilled water adjusted with KOH). It was observed that Ce significantly improved the corrosion resistance by changing the microstructure. A strong influence of Ce on the average grain size, the fraction of the eutectic, changes in morphology and/or volume fraction of gamma Al 12 Mg 17 and formation of a Cerich intermetallic phase was observed. Therefore, not only the chemical composition but also the change of microstructure and the formation of micro-galvanic elements influence the local corrosion mechanism of AZ91D with cerium.
Zinkpigmente korrodieren in einem alkalischen Gemisch aus Wasser und Butylglykol im Verhaltnis 9 : 1 unter Wasserstoffentwicklung. Die Korrosionsgeschwindigkeit nimmt dabei in der Reihe blattchenformiges non-leafing-Zinkpigment > blattchenformiges leafing-Zinkpigment > kugelformiger Farbenzinkstaub ab. Die relativ hohe Stabilitat des Farbenzinkstaubs ist auf seine deutlich geringere spezifische Oberflache zuriickzufiihren. Die Art der zur pH-Einstellung venvendeten Base hat einen deutlichen EinfluB auf die Korrosionsgeschwindigkeit des blattchenformigen leafing-Zinkpigments; die Korrosivitat fallt dabei in der Reihe Ammoniak > Natriumhydroxid > Dimethylethanolamin > Tri-0 VCH Verlagsgesellschaft mbH, D-69451 Weinheim, 1995
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