Microstructural and mechanical characterisation of 7075 aluminium alloy consolidated from a premixed powder by cold compaction and hot extrusion

• An Al–Zn–Mg–Cu alloy is processed by direct hot extrusion of a premixed powder.
• The effect of heat treatment prior to extrusion is investigated.
• As-extruded microstructure is highly dependent on the heat treatment prior to extrusion.
• The alloy extruded from presintered compact shows superior mechanical properties.

The present work concerns the processing of 7075 Al alloy by cold compaction and hot extrusion of a premixed powder. To this end, a premixed Al–Zn–Mg–Cu powder, Alumix 431D, was uniaxially cold pressed at 600 MPa into cylindrical compacts 25 mm in diameter and 15 mm thick. Subsequently, selected green compacts were subjected to either a delubrication or presintering heat treatment. Extrusion of the powder compacts was performed at 425 °C using an extrusion ratio of 25:1. No porosity was present in the microstructures of the extruded alloys. Heat treatment prior to extrusion had a great effect on the degree of alloy development in powder compacts and, as a direct consequence, remarkably affected the extrusion process and the as-extruded microstructures and mechanical properties of the processed materials. Hot extrusion caused banded structures for the alloys consolidated from the green and delubricated powder compacts. The alloy extruded from the presintered powder compact showed a fine, recrystallized microstructure which resulted in a superior combination of mechanical properties for the consolidated material.