Abstract
The effects of addition of Zr on both microstructures and mechanical properties of four advanced Al-8wt.% Zn-1 wt.% Mg-0-2.4wt.% La alloys were investigated, which had excellent stress corrosion cracking (SCC) resistance. The main results are as follows;
(1) The peripheral zone of all the extruded Al-Zn-Mg-Zr-La alloys were recrystallized with coarse grained structures, and the regions within the core were fibrous and unrecrystallized on macroscale. The core region was consisted of subgrains with low angle orientation, which were situated in layer-like colonies. For the alloys with La, the primary phase particles including elements of La and Zn dispersed in the matrix.
(2) Tensile properties of Al-8wt.% Zn-1wt.% Mg-0.1wt.% Zr with various La content were much superior to Al-8wt.% Zn-1 wt.% Mg alloy (the master alloy). Values in tensile strength were from 460 to 490MPa, and a maximum in elongation was about 11%.
(3) The crack nucleation life on the SCC tests increased with increasing La content. The core region including the fibrous structures with fine subgrains exhibited more resistant to SCC than the peripheral one with the recrystallized coarse structure.
