Superior high temperature creep resistance of a cast Al–Mg–Ca-Sc alloy with multi-scale hierarchical microstructures

The creep behavior of an Al–Mg–Ca-Sc alloy was investigated in the temperature range of 225–300 °C and applied stresses of 50–80 MPa in tension tests. Superior creep resistance was achieved as compared with those of the reported heat-resistant Al alloys. This improvement is attributed to the multi-scale hierarchy of the microstructure, i.e., Al4Ca eutectic phase network along grain boundaries (GB) and a high density of dispersed nanoscale Al3(Sc, Zr) and Al6Mn precipitates in the matrix. These nanoscale precipitates hinder dislocation motion during creep and maintain high thermal stability. The network of Al4Ca along grain boundaries plays an important role in preventing GB deformation and fracture. A stress exponent of 5 is found when introducing a threshold stress into the power-law equation, which indicates a creep mechanism of lattice diffusion controlled dislocation climb.