Effect of recrystallisation and grain size on the mechanical properties of spray formed AlCuMgAg-alloys

Investigations of spray formed AlCuMgAg-alloys containing minor additions of Ti, Zr and Mn have revealed that these alloys are prone to coarse recrystallisation during solution heat treatment. A primary recrystallisation has been observed, occurring in alloys with a zirconium (Zr) content below 0.15 wt%. Great differences between unrecrystallised and coarse recrystallised alloys have been found in the mechanical properties. Best strength and toughness values have been reached in the fine grained, unrecrystallised conditions. It is proposed that the strengthening effect in unrecrystallised alloys is based on the grain size as well as the higher density of dislocations and subgrain boundaries in the unrecrystallised material. The recrystallisation behaviour can be explained by a model which is based on the effect of particles with a bimodal size distribution. Coarse particles are necessary for the nucleation of recrystallisation and fine dispersoids control the grain growth by pinning of boundaries. Recrystallisation can be completely suppressed by a dense distribution of Zr containing dispersoids.