Melting and solidification characteristics of Zr-, Ni-, and Mn-containing 354-type Al-Si-Cu-Mg cast alloys

Abstract

ABSTRACTThis study investigated the effects of adding Zr, as a base alloying element, besides Ni and Mn in different amounts and combinations on the melting and solidification characteristics of 354-type Al-Si-Cu-Mg alloys. Differential scanning calorimetry (DSC) was used to characterise the sequence of reactions occurring during the heating and/or cooling cycles; whereas scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques were used to observe and identify existing intermetallic phases. Nickel proved to have a retarding effect on the kinetics of precipitation of the α-Al network and the eutectic Al-Si structure. Also, the presence of Ni consumed a considerable amount of Cu to form Al-Cu-Ni particles instead of Al2Cu particles. Results revealed that solution treatment at 495°C for 5 h was sufficient to dissolve a large amount of Al2Cu particles in the α-Al matrix, which is mandatory for a successful aging treatment of the alloys studied. Additions of these transition elements produced new intermetallic phases such as (Al,Si)3(Ti,Zr), (Al,Si)3Zr, Al9FeNi, Al3Ni, Al3CuNi, and Al9FeSi3Ni4Zr, in addition to the other phases, namely α-Al, eutectic silicon, Al2Cu, Mg2Si, Q-phase (Al5Cu2Mg8Si6), commonly observed in 354-type alloys, and Fe-based intermetallic phases including β-Al5FeSi, α-Al15(Fe, Mn)3Si2, and π-Al8FeMg3Si6. Superheating the melt at 800°C instead of 750°C had an advantageous effect in that Al3Zr particles originating from the Al-15%Zr master alloy were dissolved and hence coarse Zr-containing particles were barely spotted in the microstructures examined.