Abstract

In this study the changes of the hardness and microstructures during aging at 120cireC of an RS-P/M Al-5.6wt%Zn-2.0wt%Mg-1.3wt%Zr-1.0wt%Mn-0.25wt%Cu alloy were studied using a transmission electron microscopy. The hardness increased rapidly at early stage of aging and reached the maximun when the specimen was aged for 24 hr. The many irregular-shaped Al_4Mn and rod-shaped Al_6Mn dispersoids with 0.1-0.4 mum in length were observed in the as-extruded alloy. The dark particles with 2-3 nm in size were observed in aged specimen for 5hr and those are thought to be G.P.zones or precursor of eta' precipitates. In aged specimen for 24 hr, the eta' phases were distributed homogeneously within the matrix and the PFZ with 30-40 nm in width was observed along the grain boundary. With further aging, the width of PFZ increased and eta phases were also detected within the matrix.