Grain boundary strengthening in a fine grained aluminium alloy

Abstract

The present study examines the grain size dependence of yield and flow stress of the near eutectic AA8014 aluminium alloy. This alloy, when appropriately processed, can develop very fine grain sizes (d < 10[mu]m) with a uniform distribution of fine intermetallic particles. The conclusions are as follows: (1) In the present fine-grained alloy, the fine grain size is produced by pinning of grain boundaries with intermetallic particles. (2) The measured proof and flow stress data are well represented by a d[sup [minus]1] relationship rather than supporting the classic Hall-Petch equation. This d[sup [minus]1] dependence was found to be insensitive to the type of structure and thus, the high and low angle boundaries both form effective barriers to dislocation propagation. (3) In addition to the grain boundary strengthening, there is some contribution from particle hardening to the strength achieved, the effect being more pronounced at very fine grain sizes (d < 2 [mu]m). (4) The Hall-Petch constant (K), which basically measures the effectiveness of grain boundaries increasing the strength, showed a slight decrease with increasing strain, possibly due to dynamic recovery processes.