Effect of two-step increased temperature thermal rolling on anisotropy and stretch formability of AZ31 magnesium alloy sheets
(1. Shanxi Key Laboratory of Advanced Magnesium-based Materials, College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China;
2. National Engineering Laboratory for Industrial Big-data Application Technology, Chongqing Innovation Center of Industrial Big-data Co., Ltd., Chongqing 400707, China;
3. School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China;
4. Institute for Advanced Studies in Precision Materials, Yantai University, Yantai 264005, China;
5. Hunan Provincial Key Laboratory of High Efficiency and Precision Machining of Difficult-to-Cut Material, Hunan University of Science and Technology, Xiangtan 411201, China;
6. Department of Mechanical Engineering, Politecnico di Milano 20156 Milan, Italy)
2. National Engineering Laboratory for Industrial Big-data Application Technology, Chongqing Innovation Center of Industrial Big-data Co., Ltd., Chongqing 400707, China;
3. School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China;
4. Institute for Advanced Studies in Precision Materials, Yantai University, Yantai 264005, China;
5. Hunan Provincial Key Laboratory of High Efficiency and Precision Machining of Difficult-to-Cut Material, Hunan University of Science and Technology, Xiangtan 411201, China;
6. Department of Mechanical Engineering, Politecnico di Milano 20156 Milan, Italy)
Abstract: The effect of a two-step gradient thermal rolling process on the microstructure evolution and anisotropy as well as the stretch formability of AZ31 magnesium alloys was investigated. Step I was carried out at 300 °C with a small rolling reduction of 15% per pass, while the rolling temperature of Step II was 550 °C with per pass reduction of 40%. Finally, Mg alloy sheets with a thickness of 1 mm were achieved after total four rolling passes. The results indicate that shear bands are generated in rolled samples when the rolling direction is unchanged, while twinning lamellae and recrystallized grains emerge in samples when the rolling direction is changed in Step I. After Step II rolling, the size and amount of shear bands decrease, and grains are refined greatly owing to the enhanced activation of dynamic recrystallization. Besides, non-basal slips, especially prismatic áa？ slips, are found to be promoted as well based on the in-grain misorientation axis (IGMA) analysis. Therefore, improved mechanical properties, reduced anisotropy, and the improvement of stretch formability of AZ31 Mg alloy sheets are achieved.
Key words: magnesium alloy sheet; two-step increased temperature thermal rolling; non-basal slip; shear band; texture; stretch formability