Microstructure and high temperature strength of age hardenable AA2219 aluminium alloy modified by Sc, Mg and Zr additions

In the present work, it was envisaged to develop thermally stable Al-Cu alloy by modifying its chemistry. AA2219 alloys with different levels of scandium (Sc), magnesium (Mg) and zirconium (Zr) were prepared by melting with inert gas (argon) tungsten arc welding. Sc was added in three levels (0·2, 0·4, 0·8%), Mg one level (0·45%) and Zr one level (0·2%). Optical, scanning electron microscopy (SEM), X-ray diffractometry (XRD) and transmission electron microscopy (TEM) were carried out to study the microstructural details. Long time aging studies and hot tensile tests were used to study the high temperature strength of the alloys. High temperature tensile test was performed on the specimens at 250, 350 and 400uC. Room temperature tensile test was carried out for comparative purpose. Electron probe microscopy analysis (EPMA) was carried out to find out the copper segregation in the alloys. Microstructural studies showed that raising Sc content from 0·2 to 0·8% resulted in significant grain refinement. Grain refinement was much more effective with the addition of 0·2%Zr to AA2219 alloy containing 0·8%Sc and 0·45%Mg. Addition of Sc, Mg and Zr was found to increase in eutectic temperature and decrease in freezing range. Hot tensile results were found to be in agreement with results of hardness data. Among all the compositions, AA2219z0·8%Scz0· 45%Mgz0·2%Zr alloy was found to be the best in terms of its high temperature strength. © 2009 Institute of Materials, Minerals and Mining.