Effect Of Small Addition Of Sc In Artificially Aged Of Cast Al-Zn-Mg Alloy

The Al-Zn-Mg alloys were prepared through cast metallurgy route. Effects of minor scandium (Sc) on the precipitates of an age-hardenable Al-Zn-Mg alloy aged at 80 oC to 180 oC have been studied by optical microscopy (OM), differential thermal analysis (DTA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Results show that the addition of Sc in Al-Zn-Mg alloy is capable of refining cast grains obviously. Interpretation of results is done in terms of essential transformations involving GP zones, the metastable ή hardening precipitates and the stable phase η (MgZn2) respectively. Special focus has been placed on the study of microstructural evolution during initial phases of artificial ageing. Addition of Sc is found to improve the strength appreciably through strengthening mechanisms of precipitation hardening and grain refinement. This is due to the precipitation of secondary Al3Sc precipitates and noticeable grain refinement. The aim of the study is to elucidate effect of Sc on ageing kinetics of Al-Zn-Mg alloy.

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