Non-isothermal aging of a high-Zn-containing Al-Zn-Mg-Cu alloy: microstructure and mechanical properties

摘要

The non-isothermal aging behaviour of a newly developed Al-Zn-Mg-Cu alloy containing 17 wt-% Zn was investigated. Hardness and shear punch tests demonstrated that during non-isothermal aging, the mechanical properties of the alloy first increased and then decreased. The best properties were obtained in a sample which was non-isothermally agedupto 250 degrees C with heating rate of 20 degrees C min(-1), due to the presence of eta/eta (MgZn2) phases. This was confirmed by differential scanning calorimetery. After homogenisation, residual eutectic phases remained at triple junctions or in a spherical form. During aging, these phases transformed into rodlike S (Al2CuMg)-phase at 400 degrees C, with sizes ranging from 50 to 250 nm. The precipitation sequence in this high-Zn alloy was similar to that for conventional Al-Zn-Mg-Cu alloys.