Al-Zn-Mg-Cu Alloys with Strength of 800MPa

Abstract

This research has produced Al-Zn-Mg-Cu alloy containing 20%(mass fraction,the same below) alloying elements by the Hot-top semi-continuous DC casting equipment, which has adopted purifying and refining on-line technologies. This alloy has broken the limit of 7000 Al-alloy containing no more than 14% alloying elements. The microstructure and fracture of the alloy were investigated by optical microscopy (OM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM), the temperature of phases transformation was investigated by differential scanning calorimetry (DSC), and the hardness and tensile properties were also tested. The tensile strength, yield strength and elongation of this alloy can be up to 810.3, 799.3MPa and 3.4% by RRA heat-treatment after extrusion. Through the study on the single and tertiary-stage ageing treatment kinetics, the optimum ageing temperature 120℃ is identified and a wider range of aging time can be chosen. Moreover, no other precipitates are found in the alloy containing 16.1%Zn element,and the joint strengthening comes from the undissolved second phase and the ageing precipitation η' phase.

Keywords

• ultra-high strength Al alloy
• DC casting
• RRA heat treatment
• mechanical property