alloys, with the exception of the AlCu- 5NiCoZr_T7. Also, a general trend is that the higher the level of copper and magnesium, the higher the mechani- cal properties. Te same is true for the yield strength; a significant difference is observed between the lower and the highest level of magnesium for each level of copper. Again, 224 alloys with 3.6% Cu have an ambient tempera- ture UTS in the same range of the A356 family, while the higher copper versions have higher properties for all temperatures. Tere is a trade-off 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
Fig. 3. This chart shows the quality index for the alloys from 68F to 572F (20C to 300C).
AlSi5Cu3Mg_F have elongation at break lower or equivalent to that of the 224 family. Elongation of the first al- loy 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 tempera- ture. 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 tempera- tures, a significant improvement in the quality index is visible when the cop- per level increases from 3.6% to 4.6%. Other conclusions from this re-
search include: • Te 224 alloy variant with 0.15%
Mg has the highest strength across all temperature ranges in • comparison to the other alloys.
Al-Cu based alloys provide higher performance in general terms compared to conventional • Al-Si based alloys.
Te higher strength of the Al-Cu • alloys does limit the ductility.
Te quality index shows that the 224 alloys studied in this work give the best results considering • both strength and ductility.
Te 224 alloys with added dispersoids resulted in superior creep strength to similar 319 alloys under comparable loading and temperature. ■
Tis article is based on paper 14-008 that was presented at the 2014 AFS Metalcasting Congress.
40 | METAL CASTING DESIGN & PURCHASING | Jul/Aug 2015
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