Microstructure and Properties of Hot Compacted Al-12 wt% Zn-3 wt% Mg-1.5 wt% Cu Melt Spun Ribbons

Abstract

The alloys Al-12 wt % Zn-3 wt % Mg-1.5 wt % Cu with addition of Zr were melt spun and then hot pressed under 600 MPa pressure at 380 °C. Refinement of the microstructure and reduction of the volume fraction of the η (MgZn2) phase was observed in melt spun ribbon, as compared to the mould cast alloys. Good quality samples without pores and cracks obtained by hot pressing were composed of grains of size 0.2-0.5 µm. The particles of the η phase enriched in Zn, Mg and Cu were homogenously distributed in the matrix, while a few nanometres large precipitates of magnesium oxide were located at grain boundaries. Plate like precipitates of metastable h¢ phase appear after ageing at 120 °C and lead to microhardness increase up to about 195 HV as compared to 145 HV in pressed sample. Hot pressed ribbons showed compression strength of about 450 MPa which increased up to 630 MPa after ageing.