Papers by Author: Hisaki Watari

Abstract: In the present study, a two-dimensional steady state laminar flow model was developed using fluent software in order to investigate the possibility of achieving Mg/Al cladding using a horizontal twin roll caster. The effects of parameters such as upper and lower inlets casting sequence, solidification length on the temperature field at the bond interface and outlet thickness direction were investigated. The feasibility of the model was verified by combining with experiments. The results show that the molten A5052 alloy with a high melting point is more suitable to be cast by the lower roll at the roll speed of 9 m/min and the roll gap of 5 mm. The temperature of the A5052 and AZ91 near the bond interface of the clad strip can be controlled by the solidification length. Numerical simulations can provide guidance for the optimal casting process parameters.

Abstract: Al-25%Si has excellent fluidity, which allows for the casting of heat sinks with thin and tall fins. During recycling, the content of impurities such as Fe, Cu, and Mg increases. The effect of these impurities on the fluidity of the alloy was investigated. The results show that the influence of impurity elements on fluidity is small. JIS ADC12 is a popular aluminum alloy that is more economical than Al-25%Si. Si was added to ADC12 to reach a 25% Si content, producing an economical Al-25%Si. The fluidity of Si-added ADC12 was almost the same as that of Al-25%Si. Heat sinks with fin heights of 50 mm, fin top thicknesses of 0.5 mm, and a draft angle of 0.5°, were cast using the Si-added ADC12. The molten metal filled the cavity, but solidification cracks occurred when the fin top thickness was 0.5 mm. When the fin top thickness was increased to 1 mm, solidification cracks did not occur.

Abstract: The performance of three kinds of mold lubricants was evaluated by testing the flow length of Al-4.7%Mg alloy. The lubricants tested were a heat-insulating type with inorganic compounds (10~20%), a heat-insulating type with organic acid salts (~10%) and a water-soluble type with mineral oil (20~30%). The flow length of the alloy was longest when using the heat-insulating type with inorganic compounds, and shortest with the water-soluble type with mineral oil. Additionally, data variation was largest with the heat-insulating type with inorganic compounds, and smallest with the water-soluble type with mineral oil.

Abstract: Al-Si-Mg alloy strips with a Si content ranging from 0.5% to 12% were cast using a vertical type high-speed twin-roll caster at a roll speed of 60 m/min. The effect of Si content on ripple marks and cracks on the cast surface, as well as center cracks (crocodile cracks), was investigated. The results show a relationship between the Si content and these defects. When the Si content was higher than 4%, surface cracks and center cracks did not occur. However, ripple marks worsened when the Si content ranged from 3% to 5%.

Abstract: A melt drag twin-roll caster (MDTRC) was designed to convert vertical burrs at strip edges to horizontal burrs. A prototype MDTRC was assembled and tested. The forming roll is inclined frontward relative to the top of the solidification roll. Aluminum alloy strips were cast at a higher roll speed and lower roll load than what can be achieved with the conventional twin-roll caster for aluminum alloys. A semisolid layer which exists on the solidifying layer by a lower roll was formed and solidified using an upper roll. In this study, the formability of the semisolid layer and formation of horizontal burrs were investigated.

Abstract: In this study, a disk caster to cast thin bars was proposed and assembled, and the test casting of thin bars was carried out. The disk caster consists of a casting disk, a dam disk, and a tundish. A groove was machined on the side of the casting disk and, enclosed by the dam disk, acted as a mold in which to cast the bar. The diameters of the casting and the dam disks were 600 and 400 mm, respectively, and the cross-sectional area of the groove was 59.5 mm2. The casting speed was varied from 4 to 10 m/min. Molten Al–5%Mg was poured into the groove from the tundish. The groove was filled by the molten metal, and the bar could be cast continuously. The effect of the rotation speed of the dam disk on the casting of the bar was investigated.

Abstract: High-speed roll casting of AC2A aluminum alloys for casting was performed at speeds from 20 to 40 m/min using an unequal-diameter twin-roll caster to investigate the improvement of ductility and sheet forming with roll-cast strips. The width of the cast strips was 100 mm. The roll-cast strips were homogenized and cold rolled to a thickness of 1 mm, and the resulting cold-rolled strips were then annealed before tensile testing, deep drawing, V-bending, and three-roll bending. Tensile testing was also performed for a T6 heat-treated test piece. The microstructure was observed using optical microscopy.

Abstract: In Al-Si alloy roll casting, the thickness of the foil and strip decreases as Si content decreases below 2 mass%, contrary to the expectation that the latent heat decreases as Si content decreases. This phenomenon was investigated experimentally using a melt spinning single roll caster, melt drag single roll caster, and vertical type high-speed twin roll cater. The results demonstrate that the peeling of the solidification layer influences the thickness of the foil and strip. The relationship between casting conditions and adhesion of the solidification layers was also investigated.

Abstract: In a vertical type high-speed twin-roll caster, the adhesion of solidified aluminum alloy to the nozzle (ASAN) makes problems with the quality of the strip surface. The effects of the Si content of Al–Si alloys and the casting conditions on the ASAN were investigated. Alloys with Si contents of 0%, 0.5%, 1%, 2%, 3%, 6% and 10% were considered. The ASAN was high for Si contents of 0.5%, 1%, and 2%. This demonstrates that there is a relationship between the quasi-solid state and the ASAN. As the roll speed and molten metal temperature increased and solidification length decreased, the ASAN decreased. On the basis of these results, the stagnation of molten metal near the nozzle plate was investigated. A gap of 5 mm was introduced between the nozzle plate and the roll surface to eliminate the stagnation of molten metal, resulting in reduction of the ASAN.

Abstract: A three-wheel caster for the fabrication of thin aluminum alloy wire was designed, assembled and tested. The first aim was to develop a caster more compact than the Properzi continuous caster. The second was to cast thin wires without burrs. The third was for the cast wire to have a cross-sectional area of less than 80 mm². The casting of Al–Mg alloy wire was tested using the developed three-wheel caster, consisting of a large lower casting wheel and two small upper forming wheels whose positions could be independently adjusted. Two types of upper wheels were tested. The casting speed was 6 m/min, and the diameter of lower and upper wheels were 600 and 200 mm, respectively. The wheels were made from copper for the rapid solidification of the molten metal. The focus of this study was on the forming of the semisolid wire by the two upper forming wheels and the ability of the device to cast wire without burrs. The influence of the position of the upper wheels on the wire properties was investigated.