No abstract

Understanding the effects of impurities, segregation, undercooling, and solidification velocity is necessary to reconstruct prehistoric As-Cu alloy manufacturing processes and practices. Moreover, these alloys often contain a wide variety of minor and trace elements so that the binary As-Cu equilibrium phase diagram is not yet a full and adequate representation of the system in relation to arsenical bronze artifacts as-cast in ancient molds. Furthermore, the variable cooling rates in as-cast As-Cu predominant alloys due to mold material choice would have had profound effects on the formation of inversely segregated arsenic. Alloys with 1-15 wt.% arsenic were prepared and studied using differential thermal analysis (DTA), metallography, and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDXS). Equilibrium diagrams were established and the potential influence of trace elements discussed. A new liquidus curve for the equilibrium diagram in this composition range, slightly higher in temperature, was established.

No 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.

Ultrasonic treatment of aluminium melts is known as an efficient process to remove dissolved hydrogen. Whereas the degassing efficiency of ultrasonic treatment has been extensively reported, the effect of re-gassing after the ultrasonic treatment is much less studied. The present investigation attempts to evaluate the effect of artificial re-gassing of aluminium melts after ultrasonic treatment was applied. The results show an increase in porosity after artificial re-gassing after ultrasonic treatment compared to artificial gassing before the ultrasonic treatment was applied. An increase of potent nucleation sites for gas porosity after ultrasonic treatment by unfolding and/or break-up of bifilms is supposed.