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

We designed an aluminum (AD-based alloy with the alpha-Al (fcc) matrix strengthened by the T-Al6Mg11Zn11 (cubic) intermetallic phase using a large two-phase region of alpha and T phases in the Al-Mg-Zn ternary system. Thermodynamic analysis assessed a composition of Al-5Mg-3.5Zn (at%) with the alpha-Al phase reinforced with high fractions (approximately 10%) of T phase. We observed that the T phase preferentially precipitated at grain boundaries in the alpha-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 alpha-Al matrix with a particular orientation relationship of (1 - 11)(alpha)//(1 - 21)(T) and [011](alpha)//[111](T) at temperatures above 300 degrees C. After aging at 200 degrees C, numerous fine precipitates with a mean size of similar to 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 degrees C for 1 h) exhibited a high yield strength of approximately 260 MPa at 200 degrees C, much higher than those of the conventional Al alloys at elevated temperatures corresponding to service temperatures for compressor impellers in turbochargers.