Microstructure and strength of a novel heat-resistant aluminum alloy strengthened by T-Al6Mg11Zn11 phase at elevated temperatures

We designed an aluminum (Al)-based alloy with the α-Al (fcc) matrix strengthened by the T-Al6Mg11Zn11 (cubic) intermetallic phase using a large two-phase region of α and T phases in the Al-Mg-Zn ternary system. Thermodynamic analysis assessed a composition of Al-5Mg-3.5Zn (at%) with the α-Al phase reinforced with high fractions (approximately 10%) of T phase. We observed that the T phase preferentially precipitated at grain boundaries in the α-Al matrix, increasing the area fraction of the T phase at grain boundaries during aging. The granular precipitates of the T phase were dispersed rather homogenously in the α-Al matrix with a particular orientation relationship of (1−11)α // (1−21)T and [011]α // [111]T at temperatures above 300 °C. After aging at 200 °C, numerous fine precipitates with a mean size of ~20 nm in the grain interior were observed, which were likely the metastable phase associated with the T phase. The present alloy (pre-aged at 200 °C for 1 h) exhibited a high yield strength of approximately 260 MPa at 200 °C, much higher than those of the conventional Al alloys at elevated temperatures corresponding to service temperatures for compressor impellers in turbochargers.