Table 2. Tensile Properties Solutionizing at 450C (842F) YS (MPa)
front during filling would never reach a temperature below the liquidus temperature of aluminum A356 (1,135F [613C]). A pouring tempera- ture of 1,364F (740C) with a 25-sec- ond fill time was set for the conven- tional gating, and a corresponding temperature of 1,274F (690C) with a 10-second fill time was set for the direct pour arrangement. Filling with the conventional gat-
ing is shown in Fig. 4; a corresponding sketch for the direct pour filling is shown in Fig. 5. Tese two modeled fillings show conventional gating loses more superheat during filling due to heat losses in the runners and gates and due to its slower pouring rate. Te direct poured blade solidified
slightly faster because of the lower pouring temperature. Te thin edge of the blades solidified in about two minutes, while the thick end of the casting solidified in 20 minutes. Microstructures of the castings
were compared at locations L, C and
L1 L2 L3 L4 L5 C1 C2 C3 C4 R1 R2 R3 E1
155 154 159 161 163 162 158 161 168 170 165 165 165
UTS (MPa) 189 186 192 195 201 199 177 193 197 194 191 193 189
E (indicated in Fig. 6). Dendrite arm spacing was virtually the same at the three locations; however: • In the thick section (L) of the casting, the level of microporosity is less in the conventionally gated blade (0.44% vs. 0.88%).
• In the thin section of the casting, the level of microporosity is less in the direct poured blade (0.19% vs. 0.25%).
EI (%) 2.5
2.05 2.35 3.5 4.1 2.2 1.9 2.1 3.2
2.25 2.25 2.15 2.25
Q (MPa) 249 233 247 277 293 251 218 241 272 247 244 243 242
No significant differences in the
metallurgical quality of the gated and direct poured blades were noticed in spite of the much lower pouring temperature used with the direct pour technology. Te blades were given a standard T6
heat treatment consisting of solutionizing for 12 hours at 1,000F (538C), followed by quenching in 149F (65C) water and aging for six hours at 320F (160C).
August 2014 MODERN CASTING | 43
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