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presented in Table 1. The vanadium level of the 224+VZrMgCu3.6 versions is slightly lower than the target, which could be due to the settling of vanadium containing phases during batch preparation. Tensile results are presented in


3


Table 4. Alloys with 0.10% and 0.15% Mg at 4.6% Cu and alloys with 0.35% Mg at 3.6% Cu surpass all other alloys at all temperatures evaluated. Te only alloy that has yield strength proper- ties at elevated temperature, similar to those of the 224 variants, is the AlCu5NiCoZr_T7 (AA 203). An interesting point is the wide


range of yield strengths shown between the lower level of magnesium and the highest one. Tis significant difference is observed at both 3.6% Cu and 4.6% Cu, but tends to be more pronounced at higher copper level. Te researchers believe mag- nesium accelerates the rate of Al-Cu precipitation hardening reaction


Results and Conclusions The actual chemical


compositions obtained after batching the alloy in the electrical furnace are


in Al-Si-Cu(Mg) and Al-Cu(Mg) systems at these levels, which might mean the two elements behave syn- ergistically. 224+VZr4.6Cu_T7 and 224+VZr0.1Mg3.6Cu_T7 show simi- lar trends for all temperatures. Both alloys present a lower yield than that of the A356 family at ambient tem- perature, but higher at elevated tem- perature. 224+VZr0.15Mg3.6Cu_T7 shows the same trend than this lower magnesium version but with higher properties. Ambient properties are equivalent to those of the A356 family and superior at elevated temperatures. Te same pattern is observed in ultimate tensile strength (UTS). At an elevated temperature, the 224 variants show higher properties than other alloys, with the exception of the AlCu5NiCoZr_T7. Also, a general trend is that the higher the level of copper and magnesium, the higher the mechanical properties. Te same is true for the yield strength; a signifi- cant difference is observed between the lower and the highest level of magnesium for each level of cop- per. Again, 224 alloys with 3.6% Cu have an ambient temperature UTS in


the same range of the A356 family, while the higher copper versions have higher properties for all temperatures. Tere is a tradeoff between strength


and elongation at break. Te 224 alloys are not an exception to this rule and do not perform as well as other alloys. Figure 2 presents the evolution of elongation at break in function of the temperature. At room temperature, 224 alloys are not totally outclassed but, contrary to other alloy behaviors, elongation at break does not increase when the temperature augments. AlCu5NiCoZr_T7 and AlSi5Cu3Mg_F have elongation at break lower or equivalent to that of the 224 family. Elongation of the first alloy can be explained by the fact that it has high strength like 224 alloys while the low elongation of the second alloy is a result of its high iron level. Figure 3 shows the evolution of


the quality index as a function of temperature. Lower Cu versions of 224 show a quality index superior to other engine alloys for 0.15% and 0.35 % versions, but similar for the lower magnesium version (0.10%). For all test temperatures, a significant improvement in the quality index is visible when the copper level increases from 3.6% to 4.6%. Other conclusions from this


research include: • The 224 alloy variant with 0.15% Mg has the highest strength across all temperature ranges in compari- son to the other alloys.


• Al-Cu based alloys provide higher performance in general terms compared to conventional Al-Si based alloys.


• The higher strength of the Al-Cu alloys does limit the ductility.


• The quality index shows that the 224 alloys studied in this work give the best results considering both strength and ductility.


• The 224 alloys with added dispersoids resulted in superior creep strength to similar 319 alloys under comparable loading and temperature.


Fig. 3 shows the quality index for the alloys from 68F to 572F (20C to 300C). 50 | MODERN CASTING March 2015


This article is based on paper 14-008 that was presented at 2014 AFS Metalcasting Congress.


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