Influence of scandium addition on the high temperature compressive strength of aluminium alloy 7010

The influence of Sc addition on the high temperature compressive strength of a commercial alloy 7010 (hereafter termed base alloy) has been examined. The base alloy, and the base alloy with 0.23 wt% Sc were cast, homogenized and subjected to compression tests at temperatures ranging from 300 to 450 degrees C and strain rates of 10(-3), 10(-2), 10(-1) and I sec(-1). It is shown that Sc addition to the base alloy increases the compressive flow stress under these deformation conditions. The increase in peak flow stress is nearly 3-6 times the peak flow stress of the base alloy at temperatures 300-350 degrees C over the strain rate range investigated. Whilst, at temperatures >= 400 degrees C, the flow stresses decrease significantly irrespective of the strain rate used. Transmission electron microscopy (TEM) revealed that a combination of (1) increased nucleation frequency of dispersoids, (2) evolution of smaller subgrain size, and (3) refinement of alloy phases in the Al-Zn-Mg-Cu system contribute to superior strengthening in the alloy containing Sc. Whilst, it is primarily a combination of coarsening and instability of the alloy phases in the Al-Zn-Mg-Cu system that dramatically reduces the flow stresses in both the alloys at temperatures >= 400 degrees C.