Fabrication of Thin Aluminum Alloy Slab and Technological Development for Its Application

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The main purpose of this study is to fabricate a thin aluminum alloy slab using electromagnetic casting(EMC), which will enable us to make a thin plate only by cold rolling without hot rolling and intermediate annealing, . Firstly relationships between outward appearances and manufacturing conditions were investigated. Fabrication of billets as raw materials for semi-solid forming were also tried to confirm the characterization of EMC.Furthermore, mechanical properties of the rolled plates and the semi-solid formings manufactured using the EMC slabs and billets were evaluated. Obtained results are summarized as follows ;(1) At the early stage of continuous casting the meniscus thickness largely depends on the thickness of bottom block and as a result the fabricated slab thickness is nearly equal to the thickness of bottom block. When the thin slab is fabricated under a casting speed of 960mm/min and a water cooling rate of 20L/min, it has a uniform thickness of 7mm, smooth surface and … More equiaxed grains. Application of EMC to the fabrication of thin slab makes the microstructure to be very fine up to dendrite arm spacing of 10μm due to a large cooling rate caused by the thin thickness and direct water cooling. Such a fine microstructure leads to a good rolling ability up to the rolling ratio of 75% with no edge cracks.(2) Crystallized compounds increase with increase in Fe content and cooling rate, but the tensile properties of the rolled thin plate are improved because the compounds are fine and distribute uniformly and, therefore, useful for the dispersion strengthening and for refining the recrystallized grains. As a result, even when 5052 aluminum alloy contains a large amount of Fe as an impurity, tensile properties of heat-treated sheets of directly cold rolled EM cast thin slabs satisfy JIS requirements if Mg content is reduced to 2.05% which is smaller than the lower limit specified by JIS for 5052 aluminum alloy. This indicates that the application of EMC to the fabrication of the thin slab is very useful for reduction of bad influences by impurities.(3) Addition of a grain refiner and application of EMC process ensures the production of sound billets with fine and equiaxed grain throughout the entire structure. Upon semi-solid forming using the billets at optimum temperatures, fine and nearly spherical solid particles distribute uniformly throughout the formed specimens and an increase in fluidity even for thin parts are observed for all investigated alloy. Furthermore, tensile properties of T6-treated specimens of semi-solid formed samples of 7475 and A357 aluminum alloys are close to those of the forged samples of 7475 wrought alloy and A357 casting aluminum alloy sample thixocast using billets fabricated by DC casting with electromagnetic stirring, respectively. Less