Rapidly modifying microstructure and mechanical properties of AA7150 Al alloy processed with electropulsing treatment

Studies show that the proper solid solution treatment(SST)is a key step in the precipitation strengthening of AA7150 Al alloy.Despite the superior characteristics of the fully dissolved phase,it has major drawbacks,including high consumption of energy and low efficiency.Recently,electropulsing treatment(EPT)has been proposed to study dissolved precipitations and modify microstructures of AA7150 Al alloy faster than conventional SST.Experiments have been conducted in the present article,and the obtained results show that EPT can promote the rapid dissolution of theη’phase at relatively low temperatures in only 20 s.Meanwhile,the strength and ductility of electropulsed samples decrease drastically.Compared with conventional SST,EPT accelerates recrystallization and obtains relatively fine grains after 20 and 50 s electric pulses.Moreover,as the EPT time increases,the corresponding non-uniform local heating and the electron force promote dislocation generation and annihilation.

Effect of electropulsing treatment on solidification behavior of spring steels in a continuous casting mold simulator

An electropulsing-assisted mold simulator technique was developed to investigate the effects of a pulsed electric voltage on the quality of spring steels during continuous casting by analyzing the mold flux film,shell surface profile,shell micro-structure and inclusion distributions.The results revealed significantly increased crystallization fraction of the mold flux film from 61.2%to 75.3%and finer crystalline phase morphology in the case of electropulsing treatment.The surface of the initially solidified shell could be effectively healed,resulting in smoother shell surface profiles with higher pulsed voltage from 0 to 30V.Furthermore,an increase in the pulsed voltage from 0 to 30V resulted in finer dendritic structures during solidification with decreasing secondary dendrite arm spacing from the values of 17.6-32.2 to 9.7-15.0μm in the direction of shell side toward melt side.In addition,an area scan analysis of inclusions in the as-cast spring steel samples showed that the number of MnS inclusions in the size range of 2.0-4.0μm gradually decreased from 836 to 114 and the number of Al2O3 inclusions in the same size range decreased from 144 to 39,as the voltage increased from 0 to 30V.

Improving in plasticity of orthorhombic Ti_2AlNb-based alloys sheet by high density electropulsing

In order to optimize the ductility of orthorhombic Ti2AlNb-based alloys sheet,Ti22Al27Nb sheet was treated by high density electropulsing（J max =6.80 7.09 kA/mm2,tp =110 μs） under ambient condition.Microstructures were observed by SEM,and the tensile properties were also studied using uniaxial tension tests.The experimental results show that electropulsing can refine the microstructures of Ti22Al27Nb sheets.The specimen with the fine and homogeneous microstructures has good plasticity,and its elongation reaches 19.4%.The mechanism about the effect of electropulsing treatment on the microstructure of Ti22Al27Nb sheets was discussed.It was thought that the increase in nucleation rate during phase transformation and a very short treating time were regarded as the main reasons of producing smaller grains and increase in the plasticity by electropulsing.

Improvement of mechanical properties of cold-rolled commercially pure Ti sheet by high density electropulsing

Specimens cut from the cold-rolled commercially pure （CP） Ti sheet were treated by high density electropulsing （the maximum current density 7.22 kA/mm2, pulse period 110 las）. The deformation behaviors of the CP Ti specimens at different states were determined by the uniaxial tensile test. The microstructure morphologies were observed by the optical microscopy. The results show that the electropulsing induced formation of f＇me equal-axial grains and lamellar microstructures, which leads to the strength of the electropulsed CP Ti higher than that of the conventional annealed CP Ti. After electropulsing, the tensile strength and yield strength are increased by 100 MPa. And the electropulsed CP Ti has a good plasticity. The experimental results demonstrate that the electropulsing provides an effective approach to enhance the strength of cold-rolled CP Ti sheet and retain the required high ductility.

Effect of electropulsing on anisotropy behaviour of cold-rolled commercially pure titanium sheet

The specimens cut from the cold-rolled pure titanium sheet at 0°,45°and 90°to the rolling direction were treated by high density electropulsing(maximum current density J=(7.22-7.96)×10^(3)A/mm^(2),pulse period t_(p)=110μs).The mechanical properties and microstructures of the cold-rolled,electropulsed and conventional annealed commercially pure titanium sheet were examined by using uniaxial tension test machine and optical microscope(OM),respectively.The results show that the deformation behavior of the electropulsed pure titanium sheet is significantly different from that of conventional annealed pure titanium sheet.The difference of the mechanical properties between the 0°,45°and 90°direction specimens is almost diminished.It is mainly due to the increase in dislocation mobility and formation of lamellar microstructure after the electropulsing.

Extraordinary mechanical properties of AZ61 alloy processed by ECAP with 160° channel angle and EPT

AZ61 Mg alloy with homogeneous refined microstructure and exceptional mechanical properties was obtained by the combined technology of equal-channel angular pressing(ECAP)and electropulsing treatment(EPT)in this paper.Based on an ECAP die with an intersection angle of 160,the lower temperature is particularly adapted for AZ61 alloy to be deformed,in which accompanied by high accumulated defects density.The recrystallization of EPTed samples during different stages indicated that the recrystallization behavior of the deformed Mg alloy was mainly affected by the processing time and duration of EPT.Compared to those of the as-received samples,the average grain size of the EPTed samples was refined from 89μm to 1.0μm,accordingly the yields stress(YS)and ultimate tensile strength(UTS)were increased from 100 MPa and 260 MPa to 330 MPa and 448 MPa,respectively.The mechanisms of microstructure transformation and the reinforced mechanical properties were analyzed based on the strain of single ECAP,cumulative storage energy and the athermal effect of EPT.

Exceptional mechanical properties of AZ31 alloy wire by combination of cold drawing and EPT

A 0.66 mm-diameter AZ31 alloy wire with ultimate tensile strength of 400 MPa and elongation of 28.5%was successfully prepared via the combination of cold-drawing and electropulsing treatment processing(EPT).Microstructure observation showed that the grain size of EPTed samples was refined to about 1μm and the basal texture strength with maxima texture index was weakened to 7.18.EPT can significantly accelerate recrystallization by enhancing the mobility of dislocation and atomic diffusion due to the coupling of the thermal and athermal effects.Finally,uniform ultrafine-grained structure was obtained in the EPTed samples by static recrystallization completed in a very short time(30 s)at relatively low temperature(433 K).