ISSN: 1945-7553
CODEN: JTEVAB
Page Count: 7

Further Evaluation of Automated Stress Corrosion Ring (ASCOR) Testing of Aluminum Alloys

Schra, L
Senior research engineers, National Aerospace Laboratory, Amsterdam,

Wanhill, RJH
Senior research engineers, National Aerospace Laboratory, Amsterdam,

(Received 15 December 1997; accepted 5 January 1999)

Abstract

In 1991 a simple automated stress corrosion testing method called the ASCOR (automated stress corrosion ring) test was developed to test aluminum alloys according to ASTM Practice for Evaluating Stress Corrosion Cracking Resistance of Metals and Alloys by Alternate Immersion in 3.5% Sodium Chloride Solution (G 44) and using direct stressing as in ASTM Practice for Preparation and Use of Direct Tension Stress-Corrosion Test Specimens (G 49). The present investigation concentrated on evaluating two aspects of the test method: • The SCC initiation criterion (2% load decrease). • The possibility of defining a threshold stress for micro SCC growth in addition to that for macro SCC growth.

It was found that substantial SCC growth had occurred at 2% load decrease. We therefore propose reducing the load decrease criterion to 0.5% to limit the contribution of SCC growth to the SCC initiation life.

Fracture strength ratios (fracture strength of loaded exposed specimens divided by fracture strength of unloaded exposed specimens) less than 100% were found at exposure stresses below the threshold stress for macro SCC growth. Fractographic investigation showed SCC on the fracture surfaces of specimens tested at these exposure stresses. A threshold stress for micro SCC growth was determined and is defined as the exposure stress at and below which the fracture strength ratio is 100%.

Keywords:
stress corrosion, accelerated testing, constant load, threshold stress, alternate immersion, aluminum alloys, 7010-T651, 8090-T81

Paper ID: JTE12062J
DOI: 10.1520/JTE12062J
ASTM International is a member of CrossRef.