Effects of rapid heating on solutionizing characteristics of Al-Si-Mg alloys using a fluidized bed |
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Authors: | S K Chaudhury D Apelian |
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Affiliation: | (1) the Metal Processing Institute, Worcester Polytechnic Institute, 01609 Worcester, MA |
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Abstract: | Effects of rapid heat transfer using a fluidized bed on the heat-treating response of Al-Si-Mg alloys (both unmodified and
Sr modified) were investigated. The heating rate in the fluidized bed is greater than in conventional air convective furnaces.
Particle size analyses of eutectic Si showed that the high heating rate during fluidized bed solution heat treatment causes
faster fragmentation and spherodization of Si particles compared to conventional air convective furnaces. The mechanism of
Si fragmentation through fluidized bed processing is through both brittle fracture and neck formation and its propagation.
In contrast to this, the mechanism of Si fragmentation using a conventional air convective furnace is through neck formation
and propagation. The Sr-modified D357 alloy showed a faster spherodizing rate than the unmodified alloy. Thermal analyses
showed an exothermic reaction during solution heat treatment using a fluidized bed due to recrystallization, and coarsening
of eutectic Al grains. Whereas the alloy solutionized using a conventional air convective furnace showed two exothermic reactions,
one due to annihilation of point defects and the other due to recrystallization, and coarsening of the eutectic grains in
the aluminum matrix. The recrystallization temperature of the alloy solutionized in the fluidized bed is lower than those
in the conventional air convective furnace. Both tensile strength and elongation of fluidized bed solutionized alloys are
greater than those solutionized using the air convective furnace. The optimum heat-treatment time for T4 temper using a fluidized
bed for unmodified and Sr-modified alloy was reduced to 60 and 30 minutes, respectively. |
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