3
Results and Conclusions
Te morphology
of silicon is similar to that in unmodified
Al-Si alloys, but differs significant- ly from that of the fibrous mor- phology of silicon found in sodium and strontium impurity modified alloys. Te proportion of eutec- tic silicon and primary dendrite appears consistent with what is expected of the cast alloys. Figure 4 shows the load vs.
strain plot for a typical tensile sample taken from each of the Al-6%Si-1%Ba, Al-8.5%Si-1%Ba and Al-10.5%Si-1%Ba alloys. Table 1 shows how the increase in barium from 0.5% to 2.0% improved strength and decreased ductility. Figure 4 also shows alloys with lower Si content yielded lower UTS values but higher ductility. Te UTS of 145Mpa found for the Al-10.5%Si alloy is comparable to the value of about 148 MPa reported for impurity modified Al- 10%Si alloys. However, ductility of
Fig. 3. Heat treatment causes larger silicon particles in the Al-6%Si-1% Ba alloy.
the Al-10.5%Si-Ba alloys is at least 3.5 times higher than the reported alloys of about 8% Si. In fact, the ductility of any of these alloys is at least 2.5 times higher than any cur-
rent hypoeutectic casting alloys. To see the effect of heat treat-
ment, the microstructure (Fig. 3) and mechanical properties of T6 tempered Al-6%Si alloys were
Fig. 4. Shown is the load versus strain plot for samples taken from the Al-Si-1%Ba alloys with varying silicon content.
42 | METAL CASTING DESIGN & PURCHASING | Nov/Dec 2015
Fig. 5. Shown is the load versus strain plot for a sample taken from T6 heat treated Al-6%Si-1% Ba alloy.
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