STRUCTURE AND MECHANICAL-PROPERTIES OF EUTECTIC ALLOYS IN THE AL-SI-MG-NI SYSTEM

The phase diagram of the Al-Si-Mg-Ni system in the Al-Si-Mg2Si-NiAl3 c oncentration tetrahedron region is constructed. The temperatures of th e multiphase eutectic reactions and the related concentrations are det ermined. The eutectic alloys. in heat-treated state, are shown to poss ess high levels of the mechanical properties despite the presence of a substantial amount of excess phases. The results of fractographic ana lysis are used to suggest an explanation of the change of fracture mec hanism on transition from a single-phase alloy to eutectic alloys.