Characterization of Structure and Properties of As-cast AlCuMg Alloys

Abstract

Early stages of transformation of a metastable AlCuMg alloy have been studied by DSC, X-ray powder diffraction method, quantitative microstructure analysis, hardness, compression strength and by scanning electron microscope. Differential scanning calorimetry has been done for samples: AlCu15Mg1 (0%Ti), AlCu15Mg1 (0.25%Ti), AlCu15Mg2 (0.25%Ti), AlCu15Mg3 (0%Ti), AlCu15Mg3 (0.25%Ti), AlCu15Mg4 (0.25%Ti), AlCu15Mg5 (0%Ti), AlCu15Mg5 (0.25%Ti). This method has produced DSC-curve, where endothermal effects are present, on the basis of which the heat of transition has been obtained. With increasing the magnesium and titanium content in the alloy, for the first and the second detectable endothermal effect, the value of heat of transition decreases. The formation of intermetallic compounds Al₂Cu and Al₂CuMg is monitored by X-ray powder diffraction. This method has shown that a tetragonal intermetallic compound Al₂Cu and orthorhombic intermetallic compound Al₂CuMg are formed for AlCuMg alloy. 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 α-solid solution and the eutectic. In alloys containing high magnesium the average values of the DAS and grain size were found to be reduced.