Dislocation densities, dispersoid identities and the origins of thermal stability and strengthening in three mechanically alloyed aluminium alloys

Abstract

The microstructure of three mechanically alloyed dispersion strengthened Albased alloys has been investigated in the as-forged condition and after 1000 h heating at 340°C. Dislocation densities of about 10¹⁴ lines m⁻² have been measured in the as-received materials. These densities did not change significantly as a result of the above heat treatment. High resolution electron microscopy has been used to clarify the identity of the strengthening dispersoids as δ-alumina and Al₄C₃ and to determine any orientation relationship between these dispersoids and the α-Al matrix. The implications of these results for the observed thermal stability of the materials during heat treatment for up to 1000 h at 340°C and their measured hardness values are discussed.