Crack Growth Behavior of Aluminum Alloys Tested in Liquid Mercury

Abstract

Crack growth rate measurements have been made in three mercury embrittled aluminum alloys each under three loading conditions. The alloys were 1100-0, 6061-T651, and 7075-T651. The loading conditions were fixed displacement static loading, fixed load static loading, and fatigue loading at two frequencies. The results showed that mercury cracking of aluminum was not unlike other types of embrittlement (i.e. hydrogen cracking of steels). Under fixed load static conditions no crack growth was observed below a threshold stress intensity factor (KILME). At K levels greater than KILME cracks grew on the order of cm/s, while under fixed displacement loading, the crack growth rate was strongly dependent upon the strength of the alloy tested. This was attributed to crack closure. In the fatigue tests, no enhanced crack growth occurred until a critical range of stress intensity factor (ΔKth) was achieved. The ΔKth agreed well with the KILME obtained from the static tests, but the magnitude of the fatigue growth rate was substantially less than was expected based on the static loading results. Observations of the fracture surfaces in the SEM suggested a brittle intergranular fracture mode for the 6061-T651 and the 7075-T651 alloys under all loading conditions. The fractographic features of the 1100-0 alloy under fixed load and fatigue loading conditions were also brittle intergranular. Under fixed displacement loading the cracks grew via a ductile intergranular mode.

Risk analysis for operation of aluminum heat exchangers contaminated by mercury

“…One unusual aspect of LME, as opposed to other fracture processes, is that the crack propagation rates can be exceedingly rapid and the stress intensity required for crack propagation can be very low [9, 10]. Crack velocities on the order of cm/s have been measured in the laboratory.…”

“…Crack velocities on the order of cm/s have been measured in the laboratory. Theoretical and empirical studies have suggested that LME crack propagation is influenced by numerous factors that include rate of liquid mercury surface and bulk diffusion in cracks, by the concentration of Al 3 Mg 2 in grain boundaries (degree of sensitization) and by the dissolution rate of aluminum into mercury at the crack tip and by solid‐phase fracture mechanics parameters [9–14]. The rate of crack propagation tends to argue against chemical reaction and dissolution as rate controlling.…”

Stress Intensity Incubation Periods for the Al-Hg Coupled Subjected to LME

“…A variety of methods have been used to the effects of LME [12][13][14][15][16][17][18][19][20]. These tests include standard tensile, delayed fracture, slow strain rate and fracture mechanics experiments.…”

Fatigue life estimation of 1-D aluminum beam using electromechanical impedance technique

“…When a crack can be clearly identified through naked eyes, the rate was reduced to 15Hz. According to the data published by Kapp and Duquette (1986), the rate of cyclic load application between 5 ~ 30 Hz will not affect the crack growth rate of aluminum 6061-T6.…”

“…Fatigue related parameters for aluminum beam specimen (T6061-T6) dimensioned 300mm x 50mm x 6mm required for solving Equation 5.28 are tabulated in Table 5.4. Values of m and C in the Paris equation are adopted from a study conducted by Kapp and Duquette (1986).…”