THE MICROSTRUCTURE DEVELOPMENT DURING ISOTHERMAL HEAT TREATMENT STUDY OF AN Al-Mg-Si ALUMINIUM ALLOY

Abstract

The effects of isothermal heat treatment on the microstructure development of an Al-Mg-Si aluminum alloy have been investigated by means of transmission electron microscopy. From micrographs illustrating the micro structural change of the alloy during isothermal heat treatment; we can observe in the water quenched alloy sample aged for 50 and 75 hours at 350C, dispersoid particles that were aligned along <100> matrix direction losing their distribution at their early stage of precipitation with an increase in holding times. For the microstructure of the alloy ramp heated and aged at 450C for different holding times, we can clearly see dispersoid particles in their early stages of formation heterogeneously distributed with different shapes after an increase in holding times. These dispersoid particles exhibited strain field contrast when they are heated at low temperatures, that indicating they are coherent or semi-coherent with the matrix. A loss of coherency was observed for most of the dispersoid particles when they were aged with high holding times.