reference
1. Emadi, D., Whiting, L.V., Sahoo, M., Larouche, D., “Revisiting the ASTM B108 Test Bar Mold for Quality Control of Permanent Mold Cast Aluminum Alloys,” Transactions of the American Foundry Society, vol. 112, pp. 225-236 (2004).
Figure 14. With a 212F (100C) mold preheat, the porosity is absent from the tensile bars.
HigH STrengTH loW AlloY (HSlA) AluMinuM N. Johnson and P. Sanders
Michigan Technological University, Houghton, MI, USA Copyright © 2012 American Foundry Society Summary
Coherent nano precipitates of Sc and Zr trialuminides are potent strengtheners in aluminum up to 425C. As Sc is an expensive alloying addition, it is critical to optimize recov- ery during melting and casting.
To characterize Sc recovery, a crucible-melt interaction study was performed, in which magnesia, zirconia, alumina, and graphite crucibles were filled with Al-1.6wt%Sc master alloy and held at 900C for eight hours under an argon at- mosphere. After cooling, sectioning, and mounting (Fig 1), wavelength dispersive spectroscopy (WDS) line scans were performed near the crucible-melt interface. Any Sc loss to the crucible would be observed near the metallic interface, but in all four cases essentially no Sc (< 0.03 wt%) was de- tected in the crucibles (Fig. 2).
A low contact angle between the melt and the crucible can indicate a reaction may be occurring due to wetting.1
Af-
ter solidification, if the meniscus is concave, this indicates wetting, and therefore a possible reaction. All four crucible types used in this study showed convex menisci indicating that there was likely no reaction between the melt and the crucible, due to the poor wetting behavior.
Tensile and hardness testing were planned on aged Al - 0.10Sc - 0.20Zr (wt%), but the cast tensile bars showed sig- nificant shrinkage porosity and hot tearing invalidating the tensile results. Hardness values of 600 MPa were observed (Table 1), which translates to tensile strengths of about 200 MPa. In addition, homogenization before aging had no ef- fect on the final properties (Table 1).
International Journal of Metalcasting/Winter 2012
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