Research On Tensile Plastic Deformation Behavior Of Rare Earth Magnesium Alloy At Medium/High Temperature

Rare-earth magnesium alloy is one of the few and most important alloy series that can be served at high temperature among magnesium alloys.Studying its high-temperature tensile properties has extraordinary significance for guiding practical applications.Magnesium alloy parts used in the automotive and aerospace fields may collide with other objects?accidents and collisions?at different speeds to cause damage and cause catastrophic failure of the material.In addition,the use of these parts also involves different temperatures.Therefore,studying the influence of tensile loading rate and temperature on the mechanical properties of magnesium alloys is very important to ensure the reliability and durability of magnesium alloys in practical applications.In this paper,the extruded Mg-Gd-Y-Zn-Zr rare earth magnesium alloy is selected as the research object.Through the tensile tests at different strain rates and temperatures,and by means of theoretical and microscopic analysis,the characteristics of the stress-strain curve and the changing trend of mechanical properties of the alloy are described in detail,and the strain rate sensitivity and temperature sensitivity are calculated.And the plastic deformation behavior of the alloy is comprehensively discussed in combination with the deformation activation energy,activation volume and micro-morphology.Then through the research and modeling of work hardening to deepen the understanding of the plastic deformation of the alloy.According to the description of the stress-strain curve,it is found that when the test temperature is 150?,the strain rate is 10^-5/s and 10^-1/s,and the temperature is 200?,the strain rate is 10^-3/s/s and 10^-4/s.the obvious phenomenon of dynamic strain aging occurs in the sample,which may be caused by the interaction between movable dislocation,diffusive solute atom and aging precipitated phase.In the process of material softening,when the work hardening behavior and recovery mechanism compete with each other to gain the upper hand,the stress platform appears in part of the softening curve.It is found that with the increase of temperature,the strain rate sensitivity coefficient m increases,while the temperature sensitivity coefficient s decreases.However,the deformation activation energy and deformation activation volume(from 20.36(b³ at 100?to 150.07?b³ at 350??increase monotonously,and the curve is in the shape of"S".Among them,the deformation activation energy is higher than that of ordinary alloys,which may be caused by the interaction between LPSO phase and cross-slip at grain boundaries.With the increase of activation energy and activation volume,the plastic deformation mechanism gradually changes from the joint control of dislocation slip and deformation twins to the control mechanism of non-basal plane slip.Microscopically,the fracture mode also developed from intergranular fracture to a mixed mode of intergranular and transgranular.In this process,the accumulated storage energy of strain inside the tensile specimen is also released due to dynamic recrystallization.Based on work hardening index and work hardening rate,the work hardening behavior of the alloy was studied,and the plastic deformation behavior of the alloy was further expounded.It can be found that in the strain range near the yield strength,the work hardening index n increases with the decrease of temperature,but changes little with the increase of strain.According to the observation of the hardening rate-strain curve,when the temperature is less than 350?,the hardening rate increases at first and then decreases with the strain,which is due to the sharp increase of dislocation density at the initial stage of deformation.With the increase of temperature,it can be seen that there is a steady stage after the straight decline of the machining hardening rate,in which the dynamic softening is larger than the work hardening,which shows the downward of the stress-strain curve.At this stage,local unstable behaviors such as work hardening and damage compete to maintain the continuation of deformation.The work hardening of the alloy consists of the third and fourth main stages.The experimental data show that the third stage has the same sensitivity to temperature and strain rate as the fourth stage.The fourth stage has a profound impact on the change of the third stage,and the parameters involved in the two stages of work hardening are related to each other.