inside the crucible was held between 1350 and 1380F (730 to 750C). The metal was modified with strontium and grain refined with small additions of 5Ti-1B rod. Thermal analysis samples were taken every 30 minutes to ensure that the grain refinement and modification were not lost.
The resulting castings were solution heat treated for six hours at 1000F (538C) and water quenched. After a 24 hour hold at room temperature the castings were aged for 6 hours at 310F (160C). Table 3 shows the resulting mechanical property data (average of ten samples for each location). The tensile properties were considerably improved over those found in the AA study.
Values of quality index were calculated and shown in Table 3. This index will be considered in more detail later. Here we only note here that the index was proposed by French foundrymen and is defined by the formula:5
Q = UTS + 150 log E Equation 1
where Q and UTS are given in MPa and the elongation to fracture, E, is in percent. The quality index drops by about 20 % (100 MPa) at longer solidification times. It should be noted that the properties of the AA castings in Table 1 had a
An analysis of the resulting tensile data showed that the dis- solved Ti content and the boron addition had no significant effect on casting quality. The average values (56 samples for each location) and the 1σ deviation of the tensile properties are given in Table 5.
significantly lower overall level of quality index. (290 to 380 MPa, depending on section thickness).
More recently, casting trials with the AA mold were con- ducted by Alcoa at Littlestown Hardware and Foundry.6 chemistry of the base alloy used is given in Table 4.
The
The dissolved Ti level was varied between 0.01 and 0.15 wt. % by adding Al-6% Ti rod and waiting a half hour for the Ti to dissolve. Further grain refiner additions were either not made, or made as Al-3Ti-1B rod at an addition level of 20 ppm B. The melt was degassed 30 minutes with a rotary impeller degasser. Gas samples were taken at the beginning and end of each cast with a copper Ransley mold and ana- lyzed for hydrogen by a LECO analyzer. The measured gas content of all the melt samples was between 0.08 and 0.14 cc/100 grams. Castings were solution heat treated for six hours at 540C, quenched into 60C water, held 8-9 hours at room temperature, and aged six hours at 155C.
Figure 2. A356-T6 alloy tensile properties in AA test casting. Table 4. Chemistry of Base A356 Alloy
Table 5. A356-T6 Alloy Tensile Properties in Aluminum Association Mold
International Journal of Metalcasting/Winter 11
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