Stability of supersaturated solid solution of quenched Al–X (X = Zn, Mg, Cu) binary alloys

In this study, the changing trend of crystal-lattice constant and the influential factors of the stability of supersaturated solid solutions with various alloying additions in the Al–X (Zn, Mg, Cu) binary alloys were investigated. The samples were analyzed using X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), and scanning electron microscope (SEM). It is found that the addition of Cu causes the largest change of crystal-lattice constant of the Al–xCu supersaturated solid solution binary alloy. The most dramatic change occurs in the initial stage of Cu addition. The change is stabilized thereafter. Also, at the same alloying element addition to the Al–X (X = Zn, Mg, Cu) binary alloys, the Al–xCu is the most unstable system. Influential factors of the stability include the lattice constant change and the type of alloying element. The larger the lattice constant changes, the more unstable the supersaturated solid solution is. The alloying element, easy to aggregate, often leads to the solid solution less stable.