C. D. Yim, B. S. You, S. H. Kim, Korea Institute of Machinery and Materials, Changwon Gyeongnam, South Korea; Y. M. Seo, I. S. Chung, Kyungpook National University, Daegu, South Korea

Summary:

In this paper the effect of reduction ratio per pass on the microstructure and tensile properties of gravity cast and hot-rolled AZ31 alloy sheets was evaluated systematically. The thickness of as-cast plates was reduced from 10mm to around 5mm by repetitive hot-rolling at 400°C. The reduction ratio per pass changed from 10% to 50%. The deformation twins were formed mainly in large grains and finer grains evolved by dynamic recrystallization at the twin and grain boundaries during hot-rolling. The average grain sizes of sheets rolled at different reduction ratio per pass were similar but the inhomogeneity of grain size increased with reduction ratio per pass. The differences of ultimate tensile strengths and elongations of sheets fabricated with different reduction ratio per pass were not large although the yield strengths changed dramatically with reduction ratio per pass. The yield strength decreased with increasing reduction ratio per pass to 30% and then increased slightly. The ultimate tensile strengths of sheets annealed at 300°C for 1hour after rolling were similar to as-rolled sheets and the elongation increased by 40% due to annealing. The yield strengths of sheets were decreased by annealing and the difference of yield strength between as-rolled and annealed sheets was minimized at reduction ratio per pass of 30%. The interrelationship between the microstructure and tensile properties of hot-rolled AZ31 alloy sheet will be presented in more detail.