This content is not included in
your SAE MOBILUS subscription, or you are not logged in.
Galvanically Induced Atmospheric Corrosion on Magnesium Alloys: A Designed Experiment Evaluated by Extreme Value Statistics and Conventional Techniques
Annotation ability available
Sector:
Language:
English
Abstract
Galvanic corrosion of high purity die cast magnesium alloys AM50 and AZ91 was examined in accelerated atmospheric corrosion testing according to Volvo STD 1027,1375 for 6 weeks involving cycling of the relative humidity between 90% and 45% in combination with intermittent immersion in one of two NaCl-solutions (0.3% or 1.0%). The exposures were performed at two different CO2 levels; 0.01% and 0.3%.
The initial general corrosion rate of the AM50 alloy is 50-100% higher than that of AZ91 depending on surface preparation. The corrosion weight loss of both materials depends linearly on salt load in the investigated range. CO2 has a moderate accelerating effect, being higher with decreased salt load.
Extreme value analysis was used to evaluate the deepest pit distribution around the perimeter of mounted bolts in panels of AZ91 and AM50. Quite contrary to the general corrosion results, AZ91 showed 30% deeper pits than AM50. The effect of Sn/Zn coating on the attached bolts reduced pit depth with 20% compared to uncoated steel bolts. The analysis confirmed that extreme value statistics applied to pit depth measurements is a viable method to evaluate galvanic corrosion. Assessing galvanic susceptibility on the basis of total weight loss measurements is evidently misleading.
Recommended Content
| Aerospace Material Specification | Copper-Beryllium Alloy Castings 97Cu - 2.1Be - 0.52Co - 0.28Si Solution Heat Treated (TB00) |
| Journal Article | Very High Cycle Fatigue of Cast Aluminum Alloys under Variable Humidity Levels |
Topic
Citation
Isacsson, M., Ström, M., Rootzén, H., and Lunder, O., "Galvanically Induced Atmospheric Corrosion on Magnesium Alloys: A Designed Experiment Evaluated by Extreme Value Statistics and Conventional Techniques," SAE Technical Paper 970328, 1997, https://doi.org/10.4271/970328.Also In
Characteristics and Applications of Magnesium in Automotive Design
Number: SP-1250; Published: 1997-02-24
Number: SP-1250; Published: 1997-02-24
References
- Wickberg Anders Ericsson Rolf “Magnesium in the LCP 2000” SAE technical paper 850418 1995
- Melde Rolf “Volvo LCP Light Component Project” SAE technical paper 850570 1995
- Baliga C. B. Tsakiospolous P. Dept. of material science, University of surrey England UK “Design of Magnesium Alloys with improved corrosion properties” Conference. Proceedings 119 126 Garmich Partenkirchen, Germany April 1992
- Busk Robert S. “Magnesium Products Design” Marcel Dekker Book 497 499 1987
- Hawke David Ruden Thomas “Galvanic Compatibility of Coated Steel Fasteners with Magnesium” SAE technical paper 950429 1995
- Reinhold B Dr. “Beschichtungssysteme Für Verbindungselemente in kontakt mit Leichtmetallen” European Conference Corrosions protection of fasteners November 8 Paris, France 1995
- Ström M. Ström G. “A statistically Designed Study of Atmospheric Corrosion Simulating Automotive Field Conditions Under Laboratory Conditions- Final Report on the AISI Cosmetic Corrosion Set of Materials” SAE technical paper 932338 1993
- Kowaka Masamichi Dr. “Introduction to Life Prediction of Industrial Plant Material: Application of the extreme Value Statistical Method for Corrosion Analysis” 0-89864-073-3 1984 1994
- Cox D.R. Hinkley “Theoretical Statistics” 0-412-12420-3 1974