Effect of relative humidity on fatigue of anodized 2024-T351 aluminum in completely reversed torsion

A corrosion fatigue investigation was conducted on anodized 2024-T35l aluminum alloy in reversed torsion. The corrosive environment was provided by varying the relative humidity of air around the specimens during fatigue. The effect of water vapor on fatigue of aluminum (and alloys) have been previously established by other investigators. The aluminum oxide coating was grown on the metal substrate to two thicknesses (0.05 and 0.3 mils). One lot of specimens was polished to determine the effect of this type of surface finish. In all, a total of 108 specimens were run at various combinations of stress, relative humidity, coating thickness, surface finish (polishing), and coating. Six specimens were run at the stress levels of approximately 13,000, 17,000, and 20,000 lb/in² respectively. The three relative humidity ranges used were low (20-25%), medium (55-60%), and high (86-91%). Results of the investigation showed the anodized specimens at low relative humidity to have an increase in fatigue life over specimens of the same type tested at high relative humidity. The increases in fatigue lives were 281% and 194% for the 0.3 mil specimens at the highest and lowest stress levels. Increases in fatigue lives of 1112% and 338% were also found at the highest and medium stress levels for the 0.05 mil anodized specimens. It was found that the 0.3 mil anodized specimens in a relative humidity environment of 55-60% had no significant difference from those tested in an environment of 86-91%. The fatigue lives of the anodized specimens compared to results of unanodized specimens of a previous investigator at the low humidity range gave fatigue life increases of 514% and 174% at the high and low stress levels. Another comparison for anodized and unanodized specimens at high humidity showed no differences between the specimens fatigue lives. It is suggested that some phenomena is responsible for these unexpected results. That is, a humidity threshold appears to be necessary to penetrate the anodized barrier so that there is no protection of the substrate after reaching this threshold. The coating thickness of the oxide and the polishing of the specimens before anodizing showed no effect. The scatter in the investigation did not change with humidity, coating thickness, polishing or coating.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Mechanical Engineering

Department dc:contributor.department

Mechanical Engineering

Grantor dc:publisher

Virginia Polytechnic Institute and State University

Year dc:date.issued

1973

Author dc:creator

• Womack, Ernest Franklin

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Handle dc:identifier.uri

http://hdl.handle.net/10919/54834

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/54834