Effect of magnesium content on microstructure and properties of Al-Cu-Mg alloys

Abstract

The effect of magnesium content, in the range 1 - 5%, on the microstructure of aluminium - copper - magnesium alloys was examined. Using X-ray powder diffraction it was established that the tetragonal intermetallic compound Al₂Cu with lattice parameters a = 6.034 Å, c = 4.870 Å, and V = 177.31 Å3 and the orthorhombic intermetallic compound Al₂CuMg with lattice parameters a = 4.011 Å, b = 9.251 A˚, c = 7.007 Å, and V = 264.74 ų are formed across the whole range of magnesium additions. The effect of magnesium content on the microstructure was monitored quantitatively. Using automatic image analysis the linear intercept grain size, secondary dendrite arm spacing (DAS), size of eutectic cells (L _e), and the size distribution and volume fractions of α solid solution and eutectic were measured. In alloys containing high magnesium content the average values of DAS and grain size were found to decrease.