Hydrogen Embrittlement in a 2000-Series Aluminum Alloy
- PDF / 1,840,761 Bytes
- 5 Pages / 594 x 774 pts Page_size
- 33 Downloads / 195 Views
I.
INTRODUCTION
THE embrittlement of high strength aluminum alloy 7075 by cathodically charged hydrogen has been extensively investigated, 1-6 and has been observed to depend on temperature, 4 strain rate, 5 and microstructure. 4 With respect to microstructure, the dependence has been attributed to the nature and distribution of the precipitate populations. 4'6-8 Coherent G.P. (Guinier-Preston) zones in grain interiors promote planar slip, while larger and more stable precipitates promote wavy slip; 6 maximum sensitivity to both hydrogen embrittlement and stress corrosion cracking (SCC) has been correlated with a planar slip mode. 4'6-8 Other work 9,l0 has emphasized identifying the relative contribution of hydrogen to SCC susceptibility in high strength aluminum alloys. Specifically, it was found j~ that hydrogen's role in the SCC of such alloys, heat-treated to different tempers, paralleled the effect of dissolved hydrogen on the reduction of area (RA) loss in a tensile test. 4 Much of the work cited above has concentrated on the AI-Zn-Mg-Cu alloys, called "7000 series" alloys in reference to their Aluminum Association numbers. While the 7000 series alloys are the strongest class of aluminum alloys, they are approached in both strength and susceptibility to SCC by the 2000 series, A1-Cu-Mg alloys. In common with their 7000 series counterparts, these 2000 series alloys attain peak strength by virtue of a precipitate structure which is sheared rather than bypassed by dislocations. 6 However, no hydrogen embrittlement results for 2900 series alloys have been reported. This study was intended to extend the investigation of hydrogen embrittlement in high strength aluminum alloys to include 2000 series alloy compositions. Such results can be used to correlate further the involvement of hydrogen in SCC, particularly in aqueous environments. 7- l0 II.
76 mm thick, and with the composition listed in Table I. The grain structure of the plate, as shown in Figure 1, was the so-called "pancake" or disc arrangement typical of commercial product. 6 Cylindrical tensile specimens of diameter 5.4 mm and gage length 25 mm were cut from the plate with the tensile axis parallel to the longitudinal direction (RD in Figure 1). After machining, the gage length was mechanically polished to give a smooth, uniform surface finish. Abrasive papers followed by oil-based alumina compounds were used so that e x p o s u r e to water was minimized, 4 It has been reported H that by polishing aluminum alloys with waterbased slurries, large amounts, up to 100 ppm, of hydrogen can be introduced. All specimens were then given a conventional solution treatment of 20 minutes in a 490 ~ salt bath, followed by an ice-water quench. This procedure not only dissolved existing precipitates in the samples, but also annealed any mechanically-deformed surface layer resulting from the maTable I.
Cu 4.48
Composition of 2124 Plate Material (Wt Pct)
Mg 1.46
Fe 0.074
Mn 0.50
Si 0.099
Ti 0.019
Ni 0.010
A1 bal.
EXPERIMENTAL PROCEDURE
The material, supplie
Data Loading...
