THERMAL CHARACTERISTICS AND ELECTRICAL PROPERTIES OF HOT DEFORMED AA7075 ALLOYS WITH AND WITHOUT Sc, Zr ADDITIONS

Abstract

In the present work AA7075 alloys with and without Sc, Zr addition after hot deformation were studied. Thermal responses of precipitation reactions of hot deformed alloys were studied by differential scanning calorimetry, the relative electrical resistivity changes were determined by DC four-point method. The interconnections of these two materials characteristics were presented. Thermal and electrical measurements were compared to microstructure development that was observed by scanning and transmission electron microscope. Two types of eutectic phase were proved at (sub)grain boundaries. In the AA7075-Sc,Zr alloy primary multilayer Al3(Sc,Zr) particles precipitated during casting and subsequent cooling. In the thermal curves one exothermic process at ~ 200 °C and the decrease of relative resistivity changes were observed. Apparent activation energy of this process was calculated using by Kissinger method as ~ 100 kJ/mol regardless Sc, Zr addition. Schematic timetemperature-transformation diagram of the exothermic process was done on the base of calorimetric measurements at different heating rates.