| The formability of magnesium alloy is poor at room temperature,and edge cracks are easy to occur during rolling.For this reason,the local high temperature phenomenon of the high energy pulse current effect at the crack tip is used for reference to realize the dynamic suppression of edge crack in the rolling process.Electric pulse assisted rolling does not need overall heating,so it is an effective means of processing at room temperature.It is of great significance for practical production to study the temperature variation of crack tip of magnesium alloy under the action of electric pulse and to explore the establishment of a process system to restrain the edge crack of magnesium alloy rolling so as to improve the formability.In this paper,taking AZ31 magnesium alloy sheet as the object,the edge crack suppression by electric pulse assisted rolling is studied as the main line,and the following work is carried out:(1)The crack initiation and development law of magnesium alloy with different thickness during rolling at room temperature is studied.The experimental results show that the larger the initial width-thickness ratio of the plate is,the greater the reduction rate required for crack initiation and crack reaching the limit,the smaller the number of cracks and the shorter the length of cracks in the width direction when reaching the limit state.(2)The effect of electric pulse on different crack shapes was studied,the change of crack shapes after electrifying was observed,the temperature distribution on the surface of magnesium alloy plate was measured under different reduction rates,different pulse parameters and different electrifying time,and compared with finite element simulation.The results show that pulse width,pulse voltage and pulse frequency all have great influence on the temperature field of the plate surface,The finite element simulation shows that the number of cracks on the surface of the plate,the length of cracks,the voltage applied to both ends of the specimen and the application time will all affect the temperature field on the surface of the plate,and the maximum temperature difference across the width is 91.6℃.After electric pulse treatment,the crack tip of magnesium alloy specimen was obviously passivated,which inhibited the crack propagation.(3)The crack change law of magnesium alloy when the pulse parameters are changed during rolling was explored.The results show that increasing the voltage,frequency and pulse width of the electric pulse will increase the rolling temperature of the magnesium alloy specimen and reduce the crack length on the surface of the sheet during rolling.The 300V-500Hz-80μs power supply has the best effect,and the crack length is suppressed after 120 mm.In addition,the cracks of magnesium alloy specimens with different lengths can be suppressed by changing the length of the input pulse current and changing the action time of the current. |
PDF Full Text Request