Six bars per condition were pulled. For elevated temperature testing, a pretest soak at test temperature for 100 hours was applied. Since the operation temperature of these alloys is usually higher than the T7 temperature and the alloy is not stable, customers generally ask for properties from pieces which have been exposed to an elevated tem- perature for a certain time. In the present case, a 100-hour exposure time was used to allow comparison with other alloys previously designed for cylinder head applications. Bars showing inclusions in the fracture face were excluded from averages.
3
Results and Conclusions
The actual chemical
compositions obtained after batching the alloy
in the electrical furnace are present- ed 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
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. T e 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 be- tween the lower level of magnesium and the highest one. T is signifi cant diff erence is observed at both 3.6% Cu and 4.6% Cu, but tends to be more pronounced at higher copper level. T e researchers believe mag- nesium accelerates the rate of Al-Cu precipitation hardening reaction in Al-Si-Cu(Mg) and Al-Cu(Mg) systems at these levels, which might mean the two elements behave synergistically. 224+VZr4.6Cu_T7 and 224+VZr0.1Mg3.6Cu_T7 show similar trends for all temperatures. Both alloys present a lower yield than that of the A356 family at ambient
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Fig. 2. This chart shows the percent of elongation for the alloys from 68F to 572F (20C to 300C).
temperature, but higher at elevated temperature. 224+VZr0.15Mg3.6Cu_ T7 shows the same trend than this lower magnesium version but with higher properties. Ambient proper- ties are equivalent to those of the
A356 family and superior at elevated temperatures. T e same pattern is observed in ultimate tensile strength (UTS). At an elevated temperature, the 224 variants show higher properties than other
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