Abstract: The effects of the reduction per pass and the number of rolling passes on edge cracks and microstructure were investigated when the magnesium AZ31B sheets were processed by hot rolling with large reduction from slabs. The sheets were subjected to twopass or fourpass rolling at 350℃. The specimens were examined by optical microscopy， edge crack statistic and Xray diffraction. The results indicated that edge cracks appeared when the reduction rates reached 37%， and the edge crack depth increased with the increase of reduction rate. The twins also increased with the increase of the reduction rate. When total reduction rate reached 54%， most of part of the microstructure was completed.When the reduction rate increased further， shear bands appeared. For the rolling with 82% total reduction， when the rolling pass increased， the level of edge cracks decreased to some extent. Meanwhile， the basal texture changes from two basal poles to only one.

Key words: magnesium alloy, heavy reduction, rolling, edge crack, microstructure