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

本研究的主要目的是利用电磁铸造技术(EMC)制备铝合金薄板坯，使我们只需要冷轧就可以得到薄板，而不需要热轧和中间退火。首先，研究了外观与制造条件之间的关系。此外，还尝试了半固态成形用小方坯的制备，以证实EMC的特性。此外，还对轧制后的板材和用其制造的半固态成形件的力学性能进行了评价。主要研究结果如下：(1)在连铸初期，弯月面厚度很大程度上取决于底块厚度，因此铸坯厚度与底块厚度基本相等。当拉速为960 mm/m in，水冷速度为20L/m in时，薄板坯的厚度为7 mm，表面光滑，…更多的等轴晶。将电磁兼容技术应用于薄板坯的制造中，由于薄板坯的厚度和直接水冷的冷却速度较大，使得组织非常细小，达到10μm的枝晶间距。(2)随着Fe含量和冷却速度的增加，结晶化合物增多，但由于化合物细小、分布均匀，有利于弥散强化和细化再结晶组织，从而提高了轧制薄板的拉伸性能。结果表明，当5052铝合金中含有大量Fe杂质时，如果镁含量降至2.05%，低于JIS规定的5052铝合金的下限，则热处理后的冷轧EM薄板坯的拉伸性能满足JIS的要求。这表明在薄板坯的制备中应用电磁兼容技术，对于减少杂质的不良影响是非常有用的。(3)添加细化剂和采用电磁兼容工艺，保证了在整个组织中生产出细小、等轴晶的细小、等轴晶的良好铸坯。在最佳温度下使用坯料进行半固态成形时，细小且接近球形的固体颗粒均匀地分布在成形样品中，并且所有研究的合金的流动性都有所增加，即使是薄零件也是如此。此外，T6处理的7475和A357铝合金半固态成形试件的拉伸性能分别接近7475变形铝合金锻造试件和A357铝合金触变铸造试件的拉伸性能。较少

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