Influence Of Silicon Particle State On Microstructure And Mechanical Properties Of Al-Si Alloy After Severe Plastic Deformation

In order to understand the effect of Si particle state(number density and size)on dynamic recrystallization and mechanical properties of Al-Si alloy after hot deformation,three samples(1#,2#and 3#)of Al-Si eutectic alloy with different silicon particle states(the number density is decreased and the size is increased in turn)were prepared,and then were deformed by isothermal compression,hot extrusion and equal channel angular pressing(ECAP).Based on the true stress-strain curves during isothermal compression simulation,the constitutive equations were established to predict the flow behaviors of hot deformation,and the hot working maps were also drawn to optimize the hot deformation processing By OM,SEM-EBSD observations and room temperature tensile test,the influence of Si particle state on microstructures and mechanical properties were investigated.During isothermal compression deformation,all three samples with different silicon particle stales have typical steady-state flow character which is controlled by thermal activation,and the flow behavior can be accuratelypredicted by a hyperbolic sine function with Z parameter.The Si particle state has an influence on on the flow resistance and activation energy.1#sample has the highest steady-state flow resistance,then 3#and 2#.The steady-state flow activation energy is increased with the decrease in number density and the increase in size of Si particles.Based on constructed processing maps,the Si particle state has an important influence on the maximum energy dissipation coefficient and flow instability areas.In 1#sample,the maximum energy dissipation coefficient is highest among three samples,however,its peak is located at flow instability areas.The flow instability areas of 2#sample enlarges first and then decreaseswith the strainlevel,however,the energy dissipation coefficients there are low.In 3#sample,the strain has much more significant influence on the maximum energy dissipation coefficients and flow instability areas than other samples.Si particle state has a considerable influence on the microstructure evolution during hot deformation of isothermal compression,hot extrusion and ECAP.The higher the number density is(namely the smaller the particle spacing is)and the smaller the size of particles is,the higher the maturity of recrystallization,presenting as the larger the average phase difference of grains and the the percentages of high-angle boundaries,and at the same time,the larger the grain size.This indicates the fine and close Si particles can strongly promote dynamical recrystallization during hot deformation.Also,Si particle state has an influence on textures in the microstructure after hot deformation.For isothermal compression,hot extrusion,with the sample changing from 1#to 3#,the textures vary from recrystallization texture to transition texture and finally to deformation texture,but for ECAP,the deformation texture is dominant in all samples.After hot extrusion of 1#,2#and 3#sample,both tensile strength and yield strength decrease gradually with the decrease in the number density and the increase in size of Si particles,but the elongation of three samples is more than 20%.ECAP deformation results in a considerable decrease in ultimate tensile strength of three samples,but a significant rise in elongation.However,Si particle state has no obvious influence on mechanical properties after ECAP deformation.