Characterization of microstructure and properties of AlCuMg alloys

Abstract

The effect of magnesium content, in the interval range from 1 mass.% to 5 mass.%, on the microstructure and properties of aluminium - copper magnesium alloys was examined. The as-cast structure was modified by the addition of the AlTi5B1 to give alloys containing 0 to 0.25 mass. % titanium. Using X-ray powder diffraction we established that the tetragonal intermetallic compound Al2Cu and orthorhombic intermetallic compound Al2CuMg are formed across the whole range of magnesium additions. The effect of the magnesium and titanium content on the microstructure was monitored quantitatively. Using automatic image analysis we were able to measure the linear intercept grain size, the secondary dendrite arm spacing (DAS), the size of eutectic cells (Le), as well as the size distribution and volume fractions of the ?-solid solution and the eutectic. In alloys containing high magnesium the average values of the DAS and grain size were found to decrease. Also, in alloys containing high magnesium the average values of the eutectic cell length and volume fractions of the eutectic were found to increase. The changes in chemical composition of the alloy cause changes in the structure that are reflected in the Brinell hardness and the compression strength. Compression strength and hardness increase with the content of magnesium and titanium.