Papers by Keyword: Twin Roll Caster

Abstract: The solidification and process optimization for twin-roll casting of magnesium alloys have been studied. Effects of roll speed, roller diameter, setback length and strip thickness on the position of the solidification front and the surface quality of strip were analyzed through experiments. A kiss-point model which considers the strip thickness, set-back length and roll speed was established to optimize process and enhance the surface quality of magnesium alloy strip. Results showed that the twin-roll casting process could be effectively stabilized and optimized under the direction of the model, and the defectless magnesium alloy strip was obtained.

Abstract: The disadvantages of the conventional twin-roll caster for aluminum alloy are low casting speeds and limited choices of alloys that are castable by this processing. It is known that strip casting of aluminum alloy 5182 is very difficult because of their wider freezing zones. The vertical-type high-speed twin-roll caster used in the present study was devised to overcome these disadvantages. Features of the high speed twin roll casters are as below. Mild steel rolls were used in order to increase the casting speed and to be made at a lower equipment cost. Roll coating is produced in casting of Al-Mg alloy. Therefore lubricant, that resists heat transfer, was not used in the present study. Heat transfer between melt and the roll was improved by hydrostatic pressure of the melt. Low superheat casting was carried out in order to improve microstructure of the strip. In the present study, effectiveness of a high-speed twin roll caster for recycling aluminum alloy was investigated. The effects of the high-speed twin roll caster on alleviating the deterioration of mechanical properties by impurities were investigated. Properties of the cast strip were investigated by metalography, a tension test, and a deep drawing test.

Abstract: Porosity occurred in the 5182 aluminum alloy strip cast by a vertical type high speed twin roll caster. The porosity was caused by high-roll-speed and low-roll-load. Improvement of the porosity was tried by a scraper. The scraper was mounted on the roll, and the scraper was moveable depend on the thickness of the solidified layer on the roll. The scraper scribed the semisolid layer to improve the porosity. The scraper was useful to decrease the porosity of roll cast 5182 aluminum alloy strip.

Abstract: Roll casting of Al-SiCp composite alloy strip was tried using a vertical type high speed twin roll caster equipped with mild steel rolls. The Al-20vol% SiCp and Al-30vol%SiCp alloy could be roll-cast to the strip. The casting speed was 30m/min. The thickness of as-cast strip was thinner than 2.5mm. The SiCp powder was dispersed uniformly at the thickness direction. The as-cast strip could be thin down to 1mm by the hot rolling and the cold rolling without broken.

Abstract: An inline hot rolling was operated on 5182 aluminum alloy strip cast using a vertical type high speed caster (VHSTRC) at the speed of 60 m/min. A porosity existing at center line of the thickness and a ripple mark on the surface, these are typical defects of the strip cast by the VHSTRC, could be improved by the inline rolling. The rolling speed was as same as the roll-casting-speed of 60m/min. The temperature of the strip, when the inline rolling was operated, was 450oC. The reduction of the strip of the inline rolling was 35%.

Abstract: The flow stresses of AZ41M and ZK 60 wrought magnesium alloys under the deformation conditions of twin rolling casting and hot compression (TRC-HC) at different temperature and strain rates were studied. The deformation behavior and failure mechanism of them were discussed. The microstructure evolutions were analyzed by OM and EBSD technique. The results indicated that AZ41M and ZK 60 have different strain-stress curve under the same conditions. Working hardening results in occurrence of cracks in or around the shear bands. The recrystallized, equiaxed and fined grains in shear bands attribute to recovery and recrystallization, grains refinement causes local working hardening as well as decreases of crack tip driving forces. The stresses concentrate in shear bands causing cracks initiation and propagation. Casting defects to be the nucleus of cracks is another failure mode. With the increases of strains, dislocations rearrange forming sub-grains, the low angle grain boundaries (LAGBs) continuously evolved into high angle grain boundaries (HAGBs).

Abstract: In twin-roll thin strip casting, the temperature of casting roll affects the roll thermal stress, and influences the thermal deformation, the generation of roll surface cracks, the strip shape and the service life of casting roll. In this paper, the features of the casting roll materials have been analysed, the effects of the clad materials and thickness on temperature field of the casting roll have been simulated and discussed. The developed temperature model of casting roll is helpful in optimising processing parameters and the design of casting roll during twin-roll thin strip casting.

Abstract: This paper describes the twin-roll casting technology of magnesium alloys that contain relatively high weight ratios of aluminum, such as AZ91, AZ101 and AZ111. The magnesium alloy sheets were cast by a horizontal twin roll caster to manufacture relatively high-strength Mg alloys with high aluminum content. The influences of such process parameters as casting temperature and roll speed were ascertained. The microstructures of cast magnesium alloy sheets are observed to investigate the effects of roll-casting conditions on crystal growth in the cast products. It was found that Mg alloys with high aluminum content can be fabricated at a roll speed of 15 m/min with a horizontal-roll caster. The grain size of the manufactured wrought magnesium alloy sheet was about 10 micrometers due to rapid solidification in the proposed process.

Abstract: Sheets of a Mg60Cu29Gd11 alloy were produced by twin roll casting with all operational variables, except roll speed, being kept constant. As a function of the roll speed, the structure of the as-cast sheet changed from being crystalline to fully amorphous and then back to crystalline. Through careful selection of the casting speed that is suitable for the selected alloy system and with which the exit temperature of the sheet remains within the supercooled liquid region, a malleable sheet with no surface defects is produced. This work shows that twin roll sheet casting is a viable process for the production of magnesium-based bulk amorphous sheet in a continuous manner and on an industrial scale.

Abstract: Al-SiCp aluminum alloy has some useful advantages i.e., low thermal expansion, better thermal conductivity and wear resistant. Recently, plates of Al-SiCp with thickness less than 1mm was demanded. The Al-SiCp is hard and brittle. Therefore, only hot rolling was a useful process to make thin plate. In the present study, roll casting of Al-SiCp strip was tried by a vertical type high speed twin roll caster to evaluate energy savings. The Al-SiCp strip, with thickness about 2mm, was cast directly from the molten metal. The particles of SiC were dispersed uniformly. The as-cast Al-SiCp could be coiled. The roll cast Al-SiCp had superior ductility. For this reason, the eutectic Si in matrix aluminum alloy (Al-Si alloy) became fine and globular. Cold rolling could be operated after 1-pass of hot rolling. The 1mm-thick Al-SiCp plate could be made by one-pass of hot rolling and 3-passes of cold rolling and annealing from as-cast strip.