Table 1. Mechanical Properties of Al-Si-1% Ba Alloys Alloy
investigated. A comparison of this alloy with as-cast Al-6%Si- 0.5%Ba micrograph reveals two distinct features: The silicon particles have
increased in size by 10-15% due to heat treatment. The second feature relates to
the background matrix, which contains less porosity in the heat treated alloys. T e microstructural features of the heat-treated samples changed the mechanical properties. T e UTS and ductility of the heat treated samples, shown in Table 2, were noticeably improved com- pared to the as-cast samples. The mechanical properties of Al-6%Si-Ba alloys show that heat treatment increased strength by 10-15% and ductil- ity by 3-5%. The feature of mechanical properties for as- cast and T6 heat treated alloys is also evidenced in the load vs. strain plot of as-cast and T6 tempered Al-6%Si-1%Ba alloys shown in Figure 5. The microstructure of the
hypoeutectic Al-Si-Ba al- loys cast in a permanent mold exhibit high UTS and ductility values. The silicon contents of the alloys appear uniform in size and assume sub-micron flake morphology. The primary aluminum phase in the micro- structure also is very refined compared to other lightweight Al-Si alloys. The solid barium solution in silicon appears to affect the crystallization of both the primary aluminum and eutectic silicon in the hypo- eutectic Al-Si-Ba alloys when cast in a permanent mold. The effect allows the hypoeutectic melt to nucleate eutectic silicon and primary aluminum crystal, resulting in the development of high-strength, highly ductile Al-Si alloys. Also, additional improvements in alloy perfor- mance may be realized through heat treatment. ■
Al-10.5% Si Al-8.5% Si Al-5.5-6.0 % Si
2.0% Ba 1.5% Ba 0.5% Ba 2.0% Ba 1.5% Ba 0.5% Ba 2.0% Ba 1.5% Ba 0.5% Ba
UTS (MPa) 145
139 135
134 132 132
127 125 123
Ductility (%) 23
24 27
25 26 26
27 29 30
Table 2. Mechanical Properties of T6 Treated Al- 5.5-6% Si-1% Ba Alloys with Various Level of Added Ba
Alloy
Al-5.5-6%%Si-2.0%Ba Al-5.5-6%Si- 1.5% Ba Al-5.5 to 6%Si- 0.5%Ba
UTS (MPa) 142 137 133
Ductility (%) 31
35 32
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Nov/Dec 2015 | METAL CASTING DESIGN & PURCHASING | 43
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