Twinning Behavior And Precipitation Mechanism Of AZ61 Alloy During High Speed Rolling

In recent years,with the increasing awareness of environmental protection,the im portance of reducing CO₂ emissions has become increasingly prominent.Magnesium al loy has light weight,excellent performance and great potential.If it can be widely us ed,it will play an important role in energy saving and emission reduction.High spee d rolling can improve the formability of wrought magnesium alloy,reduce the defects after hot rolling,and improve the performance of magnesium alloy.In this paper,the commercial AZ61 alloy was rolled at 400?for seven passes at 1100 m/min and 275 m/min,and annealed at 400?for 10 min.By analyzing the microstructure and mechanical properties of the material after high-temperature hot rol ling,the relationship among precipitation,twinning and recrystallization behavior of ma gnesium alloy under high-speed rolling is explored,so as to further explore its plastic deformation mechanism,and provide a theoretical basis for the subsequent strengthenin g of materials.The results show that,microscopically,with the increase of passes after high spee d rolling,the internal structure of the material evolves from coarse original grains to uniformly distributed fine grains,and the main recrystallization mechanism is twin ind uced dynamic recrystallization.With the increase of strain rate,the number of nano sc ale precipitates increases gradually and the distribution becomes more uniform.The se cond phase precipitated is Mg₁₇Al₁₂,and the mechanism is strain induced dynamic pre cipitation.The nano precipitates are mainly distributed along the grain boundary and t win boundary,which can pin the recrystallized grain boundary and restrain the growth of new grains.With the increase of passes,the local strong shear bands in the materi al are restrained,which makes the overall distribution more uniform,and the composit ion of twinning gradually evolves into ultrafine grain.After inter pass annealing,comp lete static recrystallization occurs and abnormal grain growth occurs.A large number o f precipitates after rolling dissolve back in the annealing process,and the annealing st ructure is double crystal structure.Macroscopically,the surface formability of the alloy after high speed rolling at 1100 m/min is good,and there is no obvious edge crack.However,when the rolling speed decreases,with the increase of passes,the number of cracks in the material increases,which eventually leads to its fracture.It shows that different rolling speeds also have an important effect on the surface formability of the material.High speed rolling can significantly improve the formability of rolled magnesium alloy.The hardness of the material is higher after rolling at a slower speed(275 m/min),which is related to the dispersion of the second phase.With the increase of rolling passes,the hardness of AZ61 alloy increases gradually.After inter pass annealing,the material softens due to complete static recrystallization and second phase dissolution.