EXPERIMENTAL INVESTIGATION ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Al-Zn-Mg-Sc ALLOYS

Microstructures of as-cast Al-Zn-Mg alloys with and without Sc were investigated by optical microscopy, field emission scanning electron microscopy (FESEM) and energy dispersion spectrum analysis. The differential scanning calorimetry (DSC) is employed to identification the phase transformation phenomena through endothermic and exothermic reactions. The effects of Sc on the mechanical properties, recrystallization behavior and age-hardening characteristic of Al-Zn-Mg alloys were studied. The results show that the addition of Sc on Al-Zn-Mg alloy is capable of refining grains obviously. The addition of Sc can improve the strength considerably by strengthening mechanisms of precipitation and grain refinement. With the addition of Sc into Al-Zn-Mg alloy, the ageing process is quickened and the age-hardening effect is heightened. The precipitation of Al3Sc at different ageing temperatures gave significant additional hardening. The increase the strength and elongation in the alloys is related to the refine grain strengthening, precipitation particles strengthening and substructure strengthening principles