Koichi Ohori

Thermal Flow Simulation on Twin Roll Casting Process for Thin Strip Production of Magnesium Alloy

Strip continuous casting by twin roll method is a rapidly solidifying process, which can directly produce thin strips,reduce energy consumption and product cost of various metal materials. However, the casting of magnesium alloys with large solidifying ranges lead to some problems such as surface and internal defect, variation of solidification finish point for Mg sheet. In this research, the process conditions for a twin roll caster are analyzed by thermal flow simulation. The effect of type and dimension of delivery nozzles on production of Mg alloy are studied. A proper match of the setback distance of thin nozzle and casting speed is studied by thermal flow simulation, based on the characteristics of Mg melt handling, flow dynamics control and solidification.

Properties of AZ31 Magnesium Alloy Sheet Produced by Twin Roll Casting

Twin roll casting has been used to produce AZ31 magnesium alloy strip. The size of the cast strip is 5mm thick and 250mm wide. The microstructure of the as-cast AZ31 alloy strip consists of columnar zones from the surface to mid-thickness region and equiaxed zones in the mid-thickness region. The secondary dendrite arm spacing varies from 5.0 to 6.5 μm through the thickness and width of the strip and is much smaller than 34μm of an AZ31 alloy DC ingot used for comparison. In the temperature ranging from room temperature to 400°C, the tensile strength and elongation of the as-cast strip are higher and smaller than those of DC ingot, respectively. Elongation is evidently improved by homogenization treatment and becomes more than that of the DC ingot. Such an improvement of elongation is though to be caused by homogenization of segregation of Al and Zn atoms in the dendrite cell boundaries. The non-homogenized and homogenized strips were subsequently hot rolled. Their hot rolled sheets have much higher value of elongation with equivalent strength, compared to the hot rolled sheet of flat-bar extruded from DC ingot in the temperature ranging from 200°C to 300°C.

Effects of intermediate annealing on the r-value of Al-Mg alloy sheets

Abstract Effects of intermediate annealing (IA) on the r -value and recrystallization texture in 5000 series aluminum alloy sheets containing magnesium of about 5wt.% were investigated. The r -values of recrystallization annealed sheets varied with the reduction in cold rolling after IA, The 145〈321〉 type recrystallization texture was formed in the low reduction of about 10%, while the 310〈132〉 type texture was observed in the high reduction over 40%. The restoration process was also changed with an increase in the reduction, from strain induced grain boundary migration type to nucleation and growth type. In the intermediate reduction region of about 30%, the observed texture was relatively random, probably due to a mixture of both the restoration processes. The processing window, to obtain good combination of the high r -value and less anisotropy, was discussed in terms of restoration in the final annealing and the resultant texture.