Understanding Corrosion in Magnesium Die Casting Alloys

Three series of die cast corrosion test plates representing two alloy compositions and two processing methods were exposed to salt spray corrosion for various times up to 810 hours. In addition to the measurement of weight loss due to exposure, the appearance of the corroded plate surfaces was studied both macroscopically and microscopically. Numerous plates were also chemically analyzed to assist in documentation of the corrosion effects.

The most significant observation to emerge from the subject experiments was that the runner, gate and die designs established a metal flow pattern which was intimately connected with aspects of corrosion. For the test plate castings considered herein, regions of preferential pitting and boundaries separating levels of more general corrosion were both associated with reproducible metal flow patterns. Variations of composition and microstructure within the established limits for high purity die casting alloys had only secondary effects upon the corrosion behavior.