Stress-Corrosion Cracking of High-Strength Aluminum Alloys.
Abstract
A study has been made of the mechanism of hydrogen embrittlement (HE) in Al-Zn-Mg alloys, and of the role of hydrogen in the intergranular stress-corrosion cracking (I-SCC) of these alloys. Up to 300 ppm (1 at pct) hydrogen was introduced into a high-purity Al-5.6Zn-2.6Mg alloy, either by room temperature polishing with aqueous slurries of alumina particles or by exposure to water-vapor-saturated air (WVSA) at 70 C, and subsequent tensile tests (stress rate approx 0.0001/s) in inert environments caused brittle intergranular fracture. Embrittlement was found to be reversible, the tensile properties being completely restored when the hydrogen was outgassed. At low hydrogen contents, embrittlement was suppressed by the use of high strain rates (approx 0.01/s), but could not be suppressed by impact testing at large hydrogen concentrations. The intergranular fracture surfaces were observed to be associated with a fragmented layer, and electron-diffraction experiments indicated that it corresponded to a hexagonal aluminum hydride, Al H3, with a = 2.90 A and c = 4.55 A. This hydride, considered to be stress-induced, was unstable in laboratory air, slowly decomposing to FCC Al. It is concluded that internal HE in this alloy occurs by repeated cycles of the formation and rupture of this brittle hydride.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 18, 1980
- Accession Number
- ADA092186
Entities
People
- E. N. Pugh
- R. A. Yeske
Organizations
- University of Illinois Urbana–Champaign