Microstructural development of Al–15wt.%Mg2Si in situ composite with mischmetal addition

In situ Al–Mg2Si composites, as a new class of ultralight materials for aerospace and other advanced engineering applications, are attracting more and more attention of both material scientists and design engineers. It has been demonstrated in our previous work that with proper microstructural control, in situ Al–Mg2Si composites can offer very promising combinations of strength, ductility and fracture toughness. In the present work, the effects of mischmetal (MM, a mixture of rare-earth, RE elements) additions on the microstructural development of an in situ Al–15wt.%Mg2Si composite were investigated. It was found that with increasing MM additions in the composites, the size of primary Mg2Si particles was considerably reduced, and that the pseudo-eutectic Mg2Si was changed from a fibrous morphology to a flake-like morphology, showing a divorced character. A small amount of RE-containing compounds in the form of Al11RE3 were formed as a result of MM additions. It is believed that MM additions have a strong influence on the nucleation process of primary Mg2Si particles and the subsequent formation of the α-Al phase and the pseudo-eutectic matrix.