Microstructure Evolution And Mechanical Properties Of Pure Iron,Q235 Steel And 5083 Aluminium Alloy Under Cryogenic Impact Deformation

Ultrafine grained(UFG)materials possess more superior mechanical properties and wider application cases than coarse grained(CG)materials.Severe plastic deformation(SPD),such as Equal Channel Angular Pressing(ECAP),High Pressure Torsion(HPT)and Accumulative Roll Bonding(ARB)is widely used to fabricate UFG materials.Compared with common SPD method,impact deformation is simple,easy to operate and efficient to refine grains.In this paper,the effect of impact deformation and post-annealing on the microstructure and mechanical properties of pure iron,Q235B steel and 5083 aluminum alloy was investigated by means of OM,TEM,EBSD,XRD and etc.The main conclusions are as follows:(1)After cryogenic impact deformation,the grains of pure iron become finer and high density of dislocation causes dislocation cells,therefore,the grain refinement mechanisms are mainly dislocation slip and grain breaking.Besides,the tensile strength of the deformed sample increase by 75.6%while plasticity and toughness decrease.When cryogenic impacted pure iron was annealed at 580?,recrystallization occurred,which contributes to forming finer grains and spheroidized cementite.Because spheroidized cementite possesses higher plasticity,compared with as-received sample,the strength,plasticity and toughness are improved by 8.13%,15.5%and 215.7%,respectively.(2)The particle size of cryogenic impacted Q235B steel decrease from 25?m to 8?m and induced dislocations tangles forming dislocation cells.Therefore,the grainrefinement mechanism is identical to pure iron.The tensile strength of cryogenic and ambient deformed Q235B steel increase by 64.6%and 51%,respectively,while the plasticity and toughness decrease.Because of the depression of dynamic recovery,more dislocation and finer grains are obtained under cryogenic impact deformation,which means that cryogenic impact deformation possesses superior strengthening effect.(3)5083 aluminum alloy sample precipitates more second phase after cryogenic impact deformation thus enhancing the dispersion strengthening.Besides,second phase in nano size and stepped grain boundary are induced inside sample,which hinders the dislocation motion.Therefore,the grain refinement mechanism is dislocation slip.Compared with as-received material,the tensile strength of the sample is improved by 38.4%and plasticity and toughness decrease after cryogenic impact deformation.When deformed 5083 aluminum alloy sample is annealed at 200?-250?,quite a lot second phases precipitate at grain boundaries,which leads to the decrease of strength and the increase of the plasticity and toughness.When the annealing temperature is 350?,the precipitation of the second phase decreases resulting in weakness of the dispersion enhancement effect and the enhancement of plasticity.