Passage V
A molten alloy (a mixture of 2 or more metallic elements) can be poured into a cylindrical mold and cooled to form an ingot. Crystals form inside the ingot as it cools. The average crystal length, L, in micrometers (μm), determines how brittle the ingot will be. A method for reducing L using rotating magnetic fields was applied to Alloy Q as it cooled in the molds. Table 1 shows the elemental composition of Alloy Q. Figure 1 shows the effect of the relative magnetic stirring force, F, on L for ingots formed from molten Alloy Q that had an initial temperature of either 280°C or 550°C. Table 1 Percent by mass in Element Symbol Alloy Q Aluminum Al 88.7 Silicon Si 10.8 Manganese Mn 0.28 Magnesium Mg 0.22 Figure 1 102 Key 100 280°C 550°C ) 96 m ( L 94 0 10 20 30 40 50 F ( × 10 ) Figure 1 is adapted from S. Denisov, et al., “The Effect of Traveling and Rotating Magnetic Fields on the Structure of Aluminum Alloy During Its Crystallization in a Cylindrical Crucible.” ©2014 by Institute of Physics, University of Latvia.
Consider the 2 trends shown for Alloy Q initially at the temperatures of 280°C and 550°C, from F = 40 × 10 through F = 48 × 10 . If these lines were to continue along the same trend, at which of the following values of F would the average crystal lengths most likely be the same?
Correct answer: B
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