Microstructural Evolution and Mechanical Properties of Powder Hot Extruded Al-Zn-Mg-Cu Alloy

In this study, an ultrastrength Al-10Zn-3.2Mg-2.3Cu alloy was fabricated by powder hot extrusion technique. The microstructures of powder, extruded and subsequently heat treated rods were investigated by means of X-ray diffractometer (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) for compositional analysis. During extrusion, more MgZn2 compounds were precipitated from the supersaturated Al matrix and observed on the grain boundaries and in the grain interiors. The microstructure of as-extruded alloy is composed of Al matrix and MgZn2 phases in different shapes. After solution treating, the MgZn(2)phases were mostly dissolved into matrix and the major constituent are Al7Cu2Fe phase as well as oxides. The mean size of grains was controlled to 2.5 mu m, and the major precipitates were GP zones and/or eta'(MgZn2) phases in the Al matrix after peak-aging (T6) treatment (120 degrees C for 20h). The ultimate tensile strength (sigma(b)), yield strength (sigma(0.2)) and elongation (delta) are 745Mpa, 690MPa and 9.0%, respectively.