Microstructure and Mechanical Properties of an Al-Zn-Mg-Cu Alloy Processed in Semi-Solid State by Means of Twin Screw

In this study a super high-strength Al-Zn-Mg-Cu alloy was rheo- extruded by a co-rotating twin-screw extruder with different solid fractions and rotation speeds. Nominal composition of Al-14Zn-9Mg-5.2Cu and process temperature interval was thermodynamically determined. FESEM and optical microscopes were used to investigate micro structural features. Optimized combination of strength and ductility was obtained at 0.6 solid fraction and 450 rpm for screws. The mechanical properties of the rheo- extruded samples at these conditions were: UTS of 682, 621MPa 0.2% proof stress and 10% elongation.