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Influence of Humid Environment on Fatigue Behaviour of Cast AM60B Magnesium

Biallas, Gerhard and Maier, Hans Jürgen and Gall, Ken (2006) Influence of Humid Environment on Fatigue Behaviour of Cast AM60B Magnesium. In: Proc. 9th Int. Fatigue Congress. Elsevier (UK). Fatigue 2006, 2006-05-14 - 2006-05-19, Atlanta, GA (USA).

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Abstract

Low-cycle fatigue (LCF) tests were performed on cast AM60B Mg at room temperature in a high vacuum, at ambient conditions, and in 20 Torr pure water vapor (100 % relative humidity at room temperature). Surprisingly, fatigue life increased in the case of cycling in a humid atmosphere as compared to loading in vacuum. This behavior is attributed to the surface film formed on magnesium by water vapor, which suppresses slip band formation, but favors crack initiation in interdendritic regions. Consequently, only few fatigue cracks are formed early in fatigue life in water vapor, and link-up of these cracks is retarded. The number of cycles to crack initiation is much larger in vacuum environment. However, a high number of slip bands is formed early in fatigue life throughout the specimen surface. Many small cracks nucleate at these slip bands and then rapidly link-up to form the fatal crack that causes premature failure. To rationalize the effect of a humid environment, a plasticity-enhanced hydration mechanism is proposed. Hydration of the surface film on magnesium is intensified for aluminum contents below 4 wt%, which is the case for the primary α-Mg within the dendrite cells of AM60B. Plasticity-induced enhancement of the hydration prevents crack initiation at slip bands within dendrite cells in the LCF range.

Document Type:Conference or Workshop Item (Paper)
Title:Influence of Humid Environment on Fatigue Behaviour of Cast AM60B Magnesium
Authors:
AuthorsInstitution or Email of Authors
Biallas, GerhardUNSPECIFIED
Maier, Hans JürgenUniversität Paderborn
Gall, KenGeorgia Institute of Technology
Date:2006
Journal or Publication Title:Proc. 9th Int. Fatigue Congress
Refereed publication:No
In SCOPUS:No
In ISI Web of Science:No
Publisher:Elsevier (UK)
Series Name:pdf-file
Status:Published
Keywords:cast AM60B magnesium, in-situ fatigue, slip bands, small cracks, environmental degradation, surface film, hydrogen embrittlement, damage mechanisms
Event Title:Fatigue 2006
Event Location:Atlanta, GA (USA)
Event Type:international Conference
Event Dates:2006-05-14 - 2006-05-19
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Aeronautics
HGF - Program Themes:Aircraft Research
DLR - Research area:Aeronautics
DLR - Program:L AR - Aircraft Research
DLR - Research theme (Project):L - Structures & Materials
Location: Köln-Porz
Institutes and Institutions:Institute of Materials Research > Mechanical Testing of Materials
Deposited By: Dr.-Ing. Gerhard Biallas
Deposited On:23 Nov 2006
Last Modified:27 Apr 2009 04:55

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