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

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 Angstrom, c = 4.870 Angstrom, and V = 177.31 Angstrom(3) and the orthorhombic intermetallic compound Al2CuMg with lattice parameters a = 4.011 Angstrom, b = 9.251 Angstrom, c = 7.007 Angstrom, and V = 264.74 Angstrom 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-c), and the size distribution and volume fractions of alpha solid solution and eutectic were measured. In alloys containing high magnesium content the average values of DAS and grain size were found to decrease.