Investigation On Interactive Alternate Forward Extrusion Technology Of AZ31 Magnesium Alloy

Lightweight is one of the main ways to achieve energy saving and emission reduction in aerospace,rail transit,weaponry and other fields.Magnesium alloy has light weight and excellent comprehensive properties.It is one of the ideal materials for lightweight.However,magnesium alloys have a hexagonal closepacked(HCP)crystal structure.At room temperature,there are few independent slip systems that can be activated by crystals,which show poor elongation,which limits the wide application of magnesium alloys.Extrusion process is one of the important machining methods for plastic forming of magnesium alloy components.During the forming process,the deformed part is in a state of three-dimensional compressive stress and is subjected to strong shear deformation,which is beneficial to eliminate a series of defects in the structure of the processed ingot,improve the forming performance of the material.The formed products with fine-grained and excellent performance can be obtained.However,the above process still has great limitations,and there are many inconveniences in actual production and application.There is a large dead zone during the deformation process,and the material utilization rate is low;the microstructure is unevenly distributed in the cross section and the extrusion direction;the load during the processing is high and the die life is short.How to effectively solve the many problems existing in the extrusion molding process and realize the integrated precise control of the structure and properties of magnesium alloys has become a bottleneck problem in the research of magnesium alloys.Alternate extrusion process came into being on this basis,innovatively proposed discrete split punch design ideas,instead of conventional extrusion punch structure,stepwise punch loading mode changes the metal in the extrusion cylinder The flow sequence and additional shear deformation.According to the different loading cycle of the punch,it can be divided into progressive and interactive.This paper conducts a systematic study on the interactive alternating extrusion process.This paper takes the as-cast AZ31 magnesium alloy as the research object,and uses optical microscope(OM),electron backscatter diffraction(EBSD)and transmission(TEM)analysis and characterization methods to study the microstructure of interactive alternating extrusion process products,revealing The influence of different forming temperatures on the morphology of the grains was investigated.The study found that: in the range of 573 K to 673 K,the deformation mechanism during the extrusion process is significantly different,and the small grain bands formed by the fragmentation of local coarse grains coordinate metal flow The way of deformation will result in uneven tissue distribution,but slippage can promote more uniform tissue.It is worth noting that the increase in temperature promotes the enhancement of the dynamic recovery effect,and the average grain size increases.During the interactive alternating extrusion process,the main dynamic recrystallization mechanism is different at different forming temperatures,and there are many different effects on the grain morphology,but both continuous dynamic recrystallization behavior(CDRX)and discontinuous dynamic recrystallization behavior occur(DDRX),twin induced recrystallization behavior(TDRX),improved grain refinement and roundness improvement.Through a combination of finite element simulation and process experiment,the evolution mechanism of the fine-grained structure of the magnesium alloy interactive alternating extrusion was studied,and it was found that the design and distributed loading mode of the discrete split punch would form a multi-pass solid state inside the blank Stirring promotes significant grain refinement.In addition,multi-pass loading causes the c-axis of the grains to deflect in the TD direction,and some of the coarse grains in hard orientation are difficult to rotate and break,which is also an interactive alternating extrusion grain refinement mechanism.The main component,the microstructure after six-pass loading and deformation is fine and dense and all face the TD direction,and the dynamic recrystallization behavior becomes the main refinement mechanism.Finally,due to the continuous effect of the interactive alternating extrusion process on the grain orientation,the texture distribution changes accordingly.This article focuses on the influence of different process parameters on the texture weakening and texture modification,and the slip system is activated.The degree of difficulty,grain deflection and dynamic recrystallization mechanism analysis of the texture distribution law,the results show that the forming temperature and loading pass are(1-100)<11-20> cylindrical slip system and(0001)<11-20>The activation of the basal slip system has a greater influence;different dynamic recrystallization mechanisms can weaken the basal texture to a certain extent and reduce the maximum pole density.Among them,the weakening effect of twins is the most significant.