Research Of Electropulsing Treatment On Microstructures And Mechanical Properties Of Hot-rolled TC4Alloy

Titanium and titanium alloys are fine alternative armor materials of combat vehicles dueto their excellent properties such as low density, high specific strength, excellent corrosionresistance. It is well known that titanium alloys have a25%less weight than armor steelunder the same protective performance. However, titanium alloys have high susceptibilityto adiabatic shear bands and are prone to adiabatic shear failure under high strain rateloading, which have limited its application in the field of armor. Therefore, in this paper, inorder to obtain desired mechanical properties to satisfy the application needs in armor field,the effects of electric pulse heat（EPH）treatment on microstructure characteristics andmechanical properties of hot-rolled Ti-6Al-4V alloys were extensively studied. The mainconclusions are as follows:EPH treatment can make the original hot-rolled microstructure of Ti-6Al-4V alloystransform to typical lamellar microstructure within several minutes, and the minutes spentfor microstructure transformation become less with the increased heat treatmenttemperature. Before the formation of lamellar microstructure, recovery and recrystallizationhappen to the original hot-rolled microstructure; after the formation of lamellarmicrostructure, the size of beta grains and the width of alpha plates show an increasingtendency with the increased heat treatment temperature and mainting time.Compared by the original hot-rolled bimodal Ti-6Al-4V alloy, the critical failure strain ofthe recrystallized microstructure under uniaxial quasi-static compression is improved whiledecreased once the recrystallized microstructure is transformed to lamellar microstructure,so is the compressive strength. Compared by the original hot-rolled equiaxed Ti-6Al-4Valloy, the critical failure strain of the transformed lamellar microstructures under uniaxialquasi-static compression is improved, and particularly the initially transformed lamellarmicrostructure exhibits the highest critical failure strain due to the increased grain size withthe mainting time. The susceptibility to adiabatic shear bands (ASBs) of the originalhot-rolled Ti-6Al-4V alloy is obviously declined after EPH treatment, but the dynamicstrength exhibits no significant change. Compared by the hot-rolled bimodal TC4alloy, theadiabatic shear failure strain of the alloy treated at800℃for20min increases by76.6%,and the energy absorbed by specimen before adiabatic shear failure increases by75.8%.Compared by the hot-rolled equiaxial TC4alloy, the adiabatic shear failure strain of the alloy treated at1000℃for5min increases by133%, and the energy absorbed by specimenbefore adiabatic shear failure increases by192%.Microstructure analyses reveal that the low susceptibility to ASBs of specimens afterEPH treatment results from the uniform deformation zones around the main ASB and thebifurcation of the main ASB. In the EPH-treated lamellar microstructures, the uni-formdeformation of alpha colonies around the main ASB and the bifurcation of the main ASBcan release the stress concentration and consume lots of metal bulk plastic deformationwork, accordingly reduce the possibility of ASB formation and adiabatic fracture failure ofmaterials.