Abstract
Grain refinement by elemental addition has been extensively investigated within the last decades in Al or Mg alloys. In contrast, in the Cu system, the role of solute on grain size is less investigated. In this study, the grain refinement potency of several alloying elements of the Cu system was examined. To predict grain size depending on the growth restriction factor Q, grain size modelling was performed. The results obtained by the grain size model were compared to variations in the grain size of binary Cu alloys with increasing solute content under defined cooling conditions of the TP-1 grain refiner test of the Aluminium Association©. It was found that the experimental results differed significantly from the predicted grain size values for several alloying elements. A decreasing grain size with increasing alloy concentration was observed independently of the growth restriction potency of the alloying elements. Furthermore, excessive grain coarsening was found for several solutes beyond a transition point. It is assumed that contradictory variations in grain size result from a change in the nucleating particle density of the melt. Significant decreases in grain size are supposed to be due to the in-situ formation of potent nucleation sites. Excessive grain coarsening with increasing solute content may occur due to the removal of nucleating particles. The model shows that the difference in the actual number of particles before and beyond the transition point must be in the range of several orders of magnitude.
Highlights
In alloy castings, fine and equiaxed grains are desirable [1], resulting in improved mechanical properties, a reduction of defects such as microporosity, and in an improved castability [2], e.g., in an improved feeding behaviour resulting in a reduced likelihood of hot tearing
Accurately determined Q-values by cooling calculations using thermodynamic software tools were given by Cziegler and Schumacher [32]. As it was found for Al alloys [3] and Mg alloys [6] that decreasing grain size correlates with increasing Q, the objective of this study was to investigate the correlation between Q and grain size in
Grain size is plotted against the nominal alloy concentration in the range 0–1 wt %
Summary
Fine and equiaxed grains are desirable [1], resulting in improved mechanical properties, a reduction of defects such as microporosity, and in an improved castability [2], e.g., in an improved feeding behaviour resulting in a reduced likelihood of hot tearing. The final grain size of an alloy casting is dependent on the casting process; more precisely, on the cooling rate (T), the solute content, and the amount of inoculating particles [3], either via the addition of master alloys or by in situ formation. Grain refinement by inoculation has been extensively investigated for several decades [4], mainly in the field of Al alloys, both helping to understand the mechanism of grain refinement and to develop efficient master alloys, where the Al-Ti-B system is nowadays mainly used [5]. Compared to Al and Mg alloys, Cu alloys are less often investigated in the field of grain refinement [7]. Studies that have been carried out within the last decades [8,9,10,11,12,13,14,15,16,17] that are of an empirical
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