EFFECTS OF ADDITION OF TRANSITION METALS ON INTERMETALLIC PRECIPITATION IN Al-2%Cu-1%Si-BASED ALLOYS

Thermal analysis of various Al-2%Cu-1%Si alloy melts containing different transition metal additions was carried out to determine the sequence of reactions and phases formed during solidification under close-to-equilibrium cooling conditions. The main reactions observed in the base B0 alloy comprised (i) formation of the alpha-Al dendritic network at 640 degrees C, followed by precipitation of (ii) alpha-iron Al-15(Fe,Mn)(3)Si-2 phase at 620 degrees C and (iii) Al2Cu and Al5Mg8Si6Cu2 phases simultaneously as the final reaction at 495 degrees C. Two more reactions were observed with the addition of Zr, V and Ni to the base alloy, in addition to Mg2Si and AlSiTiZr, AlVTi, AlCuNi and AlCuNiFe phases. The addition of Mn (0.8%) resulted in reducing the detrimental effects of the platelet-like morphology of the beta-Al5FeSi iron intermetallic phase by replacing it with the more compact and hence less harmful script-like alpha-Al-15(Fe,Mn)(3)Si-2 phase and sludge particles. Rare earth metals have an affinity to react with certain transition metals, in particular Cu. The results reported in this study were supported by EDS, WDS and DSC analysis.