Effects of Nozzle and Roll on Surface Condition of Al-1%Si Strip Cast Using Vertical type High Speed Twin Roll Caster

When a strip of Al-Si alloy with an Si content of 1% was cast using a vertical-type high-speed twin-roll caster, cracks form in its surface. The effects of the pouring method, the shape and position of the nozzle, and the roll surface texture on surface crack formation were evaluated with a roll caster. The rolls were made of a copper alloy, and the roll speed was 30 m/min. The as-cast strips were bent to investigate the degree of crack formation, and the outer surface of the strips was observed without magnification and with a stereomicroscope to determine the influence of the pouring method, the shape and position of the nozzle, and the roll surface. A roll machined to form V-shaped grooves 0.4 mm deep on the surface of the strips was most useful for reducing surface cracking. Changing the shape of the nozzle tip was second-most effective. There was a clear correlation between the roll surface condition and surface cracking in the Al-Si strip.

High Speed Roll Caster for Aluminum Alloy

Two types of high-speed twin-roll casters and a single-roll caster equipped with a scraper were proposed. One of the twin-roll casters is a vertical-type high-speed twin-roll caster, and the other twin-roll caster is an unequal-diameter twin-roll caster. The vertical-type high-speed twin-roll caster can cast strip at speeds of up to 120 m/min. The unequal-diameter twin-roll caster casts strip at speeds up to 60 m/min. The unequal-diameter twin-roll caster is superior to the vertical-type high-speed twin-roll caster at the point of conveyance of the cast strip. A single-roll caster equipped with a scraper can cast strip without center-line segregation at speeds of up to 40 m/min. The use of a copper alloy roll and the non-use of a parting material enable high-speed roll casting. Since the roll loads of these casters are smaller than 0.1 kN/mm, soft copper alloy roll can be used. The strip does not stick to the roll without the parting material because of the use of the copper alloy roll with high thermal conductivity and the small roll load. The cooling rate near the surface is higher than 2000 °C/s.

Novel Direct Cladding of Magnesium and Aluminum Alloys Using a Horizontal Twin Roll Caster

This study introduces the direct cladding of magnesium and aluminum alloys using a horizontal twin roll caster in one step. A horizontal twin roll caster can cast a Mg/Al clad strip with thickness exceeding 5mm at a roll speed of 8m/min in one step, which is difficult for a vertical twin roll caster. Therefore, it is possible to cast a thick clad strip with different melting point alloys using a horizontal twin roll caster at low speed. It is also possible to cast clad strips using as the overlay an alloy that has a higher melting point than that of the base strips. The thickness of the Mg/Al clad strip is 6.5mm, and the ratio of the Mg layer to the Al layer is 3:2. The surface of the clad strip is good, and there is no void between bonding interfaces. The mixing layer of the bonding interface is deeply related to the reduction rate. As the reduction rate increases, the mixing layer becomes more balanced and the thickness of the mixed layer decreases to 68μm. By observation of the interface of the cladded material, the mixed layer of the bonding interface is divided into two layers. It has been found the mixed layer near the Al layer has the highest hardness (up to 228HV), and the tensile shearing strength of the manufactured Mg/Al clad strip was 44MPa.

Roll Casting and Die Casting of Si-Added Al-Mg Alloy

Si ranging from 0.2 mass% to 2.0 mass% was added to Al-5%Mg alloy (5182) and strip was cast by a vertical type high-speed twin-roll caster at a speed of 80 m/min. The as-cast strip was cold-rolled down to 1 mm thickness and annealed. The mechanical properties were investigated using cup tests and tension tests. The limiting draw ratio (LDR) of the 5182 alloy was 2.0 and the LDR became smaller as the Si content increased. When the Si content was 2.0 mass%, the LDR was 1.8, which shows that Si-added 5182 can be used for sheet forming, if the Si content is less than 2.0 mass%. The tensile strength and elongation were almost constant when the Si content was less than 1 mass%, but decreased at 2.0 mass% Si. However, the elongation was greater than 20% at 2.0 mass% Si. For die casting, 2.0 mass% Si was determined as the appropriate content from the results of the tension tests. When the Si content is in the range from 1.0 mass% to 2.0 mass%, then the Si added Al-5%Mg has the ability to be used for both die casting and sheet forming.

Changing from a Vertical Burr to a Horizontal Burr in the Vertical-Type High-Speed Twin-Roll Caster

Strip casting using a side dam plate produces a vertical burr at the strip edge. In the present study, changing this vertical burr into a horizontal burr using a burr changer is proposed. The burr changer was placed inside the side dam plate. The burr changer was made from mild steel and an insulator sheet and cut along the shape of the roll. The burr changer was placed so as to prevent exhaustion of semisolid metal between the side dam plate and the roll-side surface. When the position of the burr changer was appropriate, the vertical burr changed into a horizontal burr. The horizontal burr was flat. The width of the horizontal burr was affected by the lowest position of the burr changer and became narrower as the lowest position of the burr changer approached the roll gap position.

Reduction of Surface Cracks at Al-Mg Alloy Strip Surface Cast by Unequal Diameter Twin Roll Caster

Al-Mg alloy strips were cast by an unequal-diameter twin-roll caster. It was found that cracks formed on the surface at grain boundaries. The grains near the surface were small in size, which likely contributed to crack formation. The use of a molten metal pouring method to increase the grain size near the surface is proposed to reduce cracks. In the previous method, molten metal is poured into a pool, which is on the lower roll surrounded by side-dam plates, a back-dam plate, and the upper roll. In this study, molten metal was directly poured onto the roll surface at a shallow angle using a launder. When the angle was smaller than 20°, cracks did not form. With the proposed method, the heat transfers between the molten metal and the roll surface decreased, as determined from the grain size and strip thickness. The cracks on the strip surface were color-checked and visually inspected.

Casting of Clad Strip Consisting of Al-Sn Alloy and Pure Aluminum

Casting of clad strip consisting of Al-40%Sn-1%Cu alloy and 1050 pure aluminum from molten metals was attempted using an unequal diameter twin-roll caster equipped with a scraper. The liquidus line and solidus line of the Al-40% Sn-1% Cu alloy are 620 °C and 220 °C, respectively. The liquidus line and solidus line of the 1050 are 657 °C and 646 °C, respectively. Therefore, solidification temperatures of the two aluminum alloys are much different. When an Al-40%Sn-1%Cu solidification layer was bonded to a solidification layer of the 1050 alloy, the temperature of the 1050 solidification layer surface was higher than the solidus line of Al-40% Sn-1% Cu. However, the Al-40% Sn-1% Cu alloy could be bonded to the 1050 strip and a two-layer clad strip could be cast. The interface between the two strips was very clear. Electron Probe Microanalysis (EPMA) indicated that Sn in the Al-40% Sn-1% Cu alloy did not diffuse into the 1050 alloy. Tensile shear tests were conducted using the as cast clad strip, and no breakage occurred at the interface between the strips but only in the Al-40% Sn-1% Cu layer. This result confirmed that the two strips were strongly bonded at the interface.

Burr Formation in Casting Using Vertical-Type High-Speed Twin-Roll Caster

The mechanism and region of burr formation in casting using a vertical-type high-speed twin-roll caster were investigated using a side-dam plate with a window. A383, an aluminum alloy typically used for casting due to its excellent fluidity at semisolid condition was used. The solid fraction of the semisolid metal ejected from the window was low. When solid metal was ejected from the window, no burr formed. The results suggest that a burr formed when the semisolid metal was ejected in gap between the side-dam plate and the side surface of a roll. The semisolid metal was ejected near the point where the semisolid metal on the two rolls met.

Casting of High Aluminum Content AM Series Magnesium Alloys by Using a Horizontal Twin Roll Caster

In this paper, twin roll casting of magnesium alloys with high aluminum content such as, Mg-11 mass%Al-0.2 mass%Mn, Mg-12 mass%Al-0.2 mass%Mn, Mg-13 mass%Al-0.2 mass% have been performed for the purpose of use as an original material for hot forging. Also the mechanical properties of the cast materials were examined. A 10 miri-meters thick strip was cast by the use of a horizontal twin roll caster. The microscopic observation was conducted to investigate into the precipitation of the metal compounds such as Mg17Al12, and the Vickers hardness of the cast strips test were performed. From the result of the roll casting experiments, a 10 mm thick strip was continuously cast at a roll speed of 3.1 m/min. The average grain size of the casting strips was about 46 micron meters. When the aluminum content was 13%, the hardness of the twin roll cast (TRC) strips became 1.7 times higher than that of extruded AZ 31. Also, a uniaxial compression test at elevated temperature was conducted to obtain a true strain-true stress curve for examining possibility of direct hot forging (DHF) of TRC magnesium alloys with high aluminum content.

Investigation of Burr on Strips Cast by Vertical-Type High-Speed Twin Roll Caster

The factors affecting the shape and size of burrs that form at the edges of strips cast by a vertical type twin roll caster were investigated in this study. The size of the burr was found to be affected by the Si content of the strip. When the Si content was larger than 7 mass%, the burrs became larger. The position of the lower edge of the side dam plate also affected the shape of the burr. The burrs that formed were generally perpendicular to the strip surface but changed to being parallel to the strip surface as the position of the lower edge of the side dam plate was displaced upward from the center of the rolls.