On the Hall–Petch relationship in a nanostructured Al–Cu alloy

Mechanical properties of bulk nanocrystalline Al–4Cu alloys with grain sizes from 47 to 105 nm, synthesized by mechanically alloying followed by vacuum hot pressing at different temperatures, were analysed through Hall–Petch relation. Hall–Petch analysis revealed a high frictional stress (170 MPa) and a high positive slope ( 0.13   MPa   m ) as compared to pure Al, which has a frictional stress (15–30 MPa) and a slope ( 0.06 – 0.09   MPa   m ). From a detailed evaluation of different strengthening mechanisms it is inferred that the Al2Cu precipitates and oxide particles are the likely reason for such high values of frictional stress and slope.