Effect of thermo-mechanical treatment on microstructure and tensile properties of 2219ScMg alloy

An improved high temperature performance of 2219 aluminium alloys through thermo-mechanical treatments having additions of 0.8 wt% Sc and 0.45 wt% Mg is presented. The copper mould chill cast alloy designated as 2219ScMg is processed through two different routes. In the first route, designated here as HMCR process, the alloy is homogenised at 530 degrees C and cold rolled, while in the second route, designated here as HRCR process, the cast alloy is directly rolled sequentially under hot and cold conditions. The evolution of the microstructure and strength are examined throughout the processes. The formation of L1(2) ordered Al3Sc and Al-3(Sc, Zr) precipitates of average size 10 +/- 5.5 nm (radius) takes place during solidification. In the HMCR process, homogenization of the alloy at 530 degrees C results in an increase in the number density of these precipitates in addition to partial dissolution of copper in the Al matrix. Subsequent cold rolling of the alloy introduces strain hardening. The same thing happens during hot rolling at 300 degrees C in HRCR process but the size of the Al3Sc/Al-3(Sc, Zr) precipitates is smaller. The subsequent cold rolling again strain hardens the alloy. In addition to excellent room temperature 0.2% proof stress of similar to 500 MPa in both the processes, outstanding elevated temperature (200 degrees C) 0.2% proof stress of 345 MPa in HMCR and 312 MPa in HRCR is obtained. Thermal stability of the alloy at elevated temperature is enhanced by the Sc and Mg segregation at the Al/theta' interface and the formation of a small amount of Omega phase.