Hot Deformation Behavior Of Mg-4Sm-2Zn-0.5Zr Alloy And Its Extrusion Process And Structure Property

Magnesium alloys are widely used in the aerospace,automotive and electronic industries,for their low density,high specific strength and other excellent properties.With the development of technology and national defence,more and more demands on high-performance and light-weight magnesium alloys are proposed.On the one hand,rare earth elements have the great strengthening effect on magnesium alloys,but the high cost of Mg-Re alloy has always drastically restricted its application.On the other hand,wrought magnesium alloys have better mechanical properties than cast magnesium alloys.In order to meet the need for new low-cost heat-resistant magnesium alloy,we has developed Mg-4Sm-2Zn-0.5Zr alloy by ourselves.And studying hot deformation behavior of the alloy can provide guidance for the processing design.In this paper,the constitutive model and processing map of Mg-4Sm-2Zn-0.5Zr alloy were studied by isothermal compression experiment.Then the hot extrusion process was explored based on the processing map,microstructural analysis and mechanical properties testing of the alloy were carried out.The main research contents and results are as follows:(1)The stress-strain curve of Mg-4Sm-2Zn-0.5Zr alloy at temperature of 350-450°C and strain rate of 0.001-1s-1 was obtained by isothermal compression experiment.Based on the curve,it could be found that the flow stress decreases with the increase of temperature and the decrease of strain rate.According to the obtained experimental data,the Arrhenius constitutive equation based on peak stress strain was established at first,then the modified equation considering all of strain was also established by fitting the material parameters.The comparison of calculated results with measured data verified the effectiveness of the models.(2)With Matlab software,the strain rate,temperature and strain as the input,the flow stress as the output,the constitutive model of Mg-4Sm-2Zn-0.5Zr alloy using BP neural network model was proposed by setting the network parameters.On this foundation,by using genetic algorithm(GA)and particle swarm optimization(PSO)optimize the weight and threshold of BP network,the GA-BP model and PSO-BP model were put forward.(3)The processing map based on neural network model and Muthy instability criterion had been established.And in view of the effects of strain,the 3D processing map had been established.According to the distribution of power dissipation efficiency and instability zone,in combination with microstructural analysis,the optimum processing parameters were determined.(4)Aiming at the optimal temperature and strain rate that obtained from the processing map,the optimal process parameters of extrusion were obtained by numerical simulation of the extrusion process under different initial temperature and extrusion speed.In addition,the microstructure analysis and the mechanical properties testing of Mg-4Sm-2Zn-0.5Zr alloy were carried out.