Characterization of quasicrystalline precipitates in artificially aged Al–Mg–Zn alloy with Ga addition

Abstract

This work present studies on microstructures and mechanical properties of two conventionally cast Al–Mg–Zn base alloys subjected to aging process: Al-2.7Mg-2.1Zn and Al-2.2Mg-1.8Zn-1.1Ga (at.%). Both alloys were homogenized, solution treated and aged isothermally at 473 K (200 °C). Maximum hardness in the base and the Ga-modified alloy was reached after 4 h of aging, however the Ga–bearing sample demonstrated much higher hardness values and tensile strength. The difference correlates with the high precipitate number density estimated for this sample. Based on electron diffraction data, the structure of formed precipitates differs between the ternary and the Ga-modified material. Studies using a transmission electron microscope (TEM) indicated that η and η′ precipitates are present in the peak-aged microstructure of the Al-2.7Mg-2.1Zn alloy, while in the Ga-bearing sample icosahedral quasicrystalline and T-phase precipitates are formed. A crystallographic relationship between the I-phase precipitates and the Al matrix were analyzed in detail along different zone axes of the Al lattice.

Keywords

• Aluminium alloys
• Precipitation hardening
• Transmission electron microscopy
• Quasicrystals