Suppression Of Edge Crack Of Cold Rolled Magnesium Alloy By High Pulse Current And Its Mechanism Analysis

Magnesium alloys are abundant in our country.However,due to the close-packed hexagonal structure of magnesium alloys and the characteristics of non-base surface sliding and not moving at room temperature,the plastic processing of magnesium alloys is difficult,and there are many defects and secondary processing difficulties after forming.Taking the rolling of magnesium alloy sheet and strip as an example,edge cracking has always been a prominent problem that puzzles production.Although hot rolling and warm rolling processes have been improved,they are complex,energy-consuming and inefficient.In order to adapt to the national green development ideas,it is urgent to study new rolling processes.Electro-plastic effect is a unique phenomenon that the metal deformation resistance decreases rapidly and the plasticity increases by introducing appropriate pulse current in the process of metal deformation.Compared with traditional processing technology,electro-plastic processing has obvious advantages,such as processing at lower temperature,improving the mechanical properties of forming parts,improving efficiency and reducing energy consumption,especially for the deformation of refractory metals.Aiming at the phenomenon of edge cracks in magnesium alloy rolling process,this paper introduces high energy pulsed current rolling,and puts forward a new rolling technology which can effectively restrain cracks in magnesium alloy rolling at room temperature.Through the construction of electric pulse rolling experimental platform and multi-case rolling experiment,combined with rolling micro-morphology and macro-mechanical test analysis,the inhibition ability and mechanism of electric pulse field on magnesium alloy rolling edge cracking were studied.The application lays the theoretical foundation and experimental basis.In this paper,the warm rolled magnesium alloy strip is taken as the object of study.(1)The rolling deformation limit at room temperature is studied.The experimental results show that the edge cracks occur in the rolled magnesium alloy at 8% reduction.The edge cracks are obvious when the reduction is increased to 25%,and the fracture of the magnesium alloy strip begins at 30% reduction.(2)To investigate the effect and regularity of high-energy pulse current assisted rolling on edge crack suppression of magnesium alloy strip and its effect on micro-structure and rolling force,it is found that high-energy pulse current significantly inhibit the occurrence of edge crack.With the increase of current intensity,frequency and pulse width,the number,depth of edge crack and rolling force and V-shaped shear band in micro-structure are decreased to different extents.(3)Electroplastic rolling of homogenized magnesium alloys is carried out.The effects of different current intensities on edge cracks,rolling force,microstructure and mechanical properties of magnesium alloys are investigated experimentally.The results show that the plasticity of magnesium alloy after homogeneous treatment is significantly improved,no obvious edge cracks appear in 25% reduction,and the rolling force decreases with the increase of current intensity.The change of microstructures is different under different reduction conditions,and the change of microstructures is basically the rule of microstructural refinement.Tensile strength and yield strength increase with the increase of current strength,while hardness decreases with the increase of current strength.(4)Through in-situ electrification observation of edge cracks,it is found that under certain current parameters,cracks are obviously compressed and cracks narrow.The mechanism of high-energy pulse current inhibiting edge cracks in magnesium alloy rolling is further explored,and a new rolling process for improving rolling efficiency and mechanical properties of magnesium alloy at room temperature is proposed.In this paper,the effects of different electrical parameters of high-energy electric pulse on macro-edge cracks of magnesium alloys are studied,and its mechanism is briefly analyzed.However,due to the effect of pulse current mainly on the atomic level and the rapid dynamic impact,there is no suitable method to observe directly at present,so further research is needed.