Effect of surface treatment on fatigue properties of Al–Li–Cu–Mg–Zr and Al–Zn–Mg–Cu–Zr plate

Relationship of microstructure to fatigue strength loss in anodised aluminium–copper alloys

“…Figure 5 shows that the pitting from anodisation resulted from preferential dissolution of the Cu rich constituent that remained distributed intragranularly and intergranularly in the material as a casting artefact. This was in concert with Keller et al, 10 aluminium-zinc based alloys, 12 and with aluminiumlithium alloys, 13 where in the latter two cases, dissolution of grain boundary precipitates was found to be the principal cause of fatigue strength losses following anodisation.…”

“…Other work on an aluminium-lithium alloy of similar composition to AA8090 showed minor fatigue strength loss following a pickle and anodise process that dissolved grain boundary precipitates. 13 Note that the grain boundary precipitation appeared to be much greater for Fox et al 13 than for Gregson et al 12 The literature presents limited fatigue data for anodised Al-Cu. To the anodiser, the 2000 series Al-Cu alloys represent the greatest challenge.…”

“…The influence of constituent at the grain boundary on fatigue strength has been observed in Al-Li and Al-Zn alloys AA8090 and AA7010. 12 AA7010, with more grain boundary constituent than AA8090, experienced fatigue strength loss, compared with improved fatigue strength AA8090. Other work on an aluminium-lithium alloy of similar composition to AA8090 showed minor fatigue strength loss following a pickle and anodise process that dissolved grain boundary precipitates.…”

Editorial

“…Gregson et al 76 discussed the role of vacancies in the precipitation of d9-and S-phase in Al-Li-Cu-Mg alloys and noted that the very high binding energy between Li atoms and vacancies had a marked effect on the precipitation sequence and kinetics (features that were later expanded upon in two excellent papers by Huang and others on the effects of Li additions to AA 6061 77,78 and to AA 7075 alloys 79 to just three. In a useful study of the effect of surface treatments (pickling and shot peening) on fatigue performance of AA 8090 and AA 7010 (with no Li addition), Gregson et al 81 found that 8090 was less susceptible to chromic/sulphuric pickling than 7010; this was attributed to the more homogeneous microstructure of the Li containing alloy that led to a smoother surface. The other two papers, Srivatsan and Coyne 82 and Prasad and Rao, 83 both investigate low cycle fatigue behavior of Li containing alloys and show a bilinear Coffin-Manson power law relationship for Li additions above about 2?5 wt-%, attributed to changes in deformation mode.…”

“…Of the small number of papers in MST on mechanical behaviour of Li-containing alloys, I draw attention to just three. In a useful study of the effect of surface treatments (pickling and shot peening) on fatigue performance of AA 8090 and AA 7010 (with no Li addition), Gregson et al 81 found that 8090 was less susceptible to chromic/sulphuric pickling than 7010; this was attributed to the more homogeneous microstructure of the Li containing alloy that led to a smoother surface. The other two papers, Srivatsan and Coyne82 and Prasad and Rao,83 both investigate low cycle fatigue behavior of Li containing alloys and show a bi-linear Coffin–Manson power law relationship for Li additions above about 2·5 wt-, attributed to changes in deformation mode.…”