Fabrication Process And Properties Of Fe-6.5wt.%Si Alloy Wires

Fe-6.5wt.%Si alloy(high silicon electrical steel)is an excellent soft magnetic material with high permeability,high resistivity,low iron loss and near-zero magnetostriction,which can save much energy,and reduce noise in service.With the feature of compression in radial direction and elongation in axis direction during drawing,the deformation of this alloy is relatively easy for drawing.Moreover,the relatively small cross sectional area of wires is useful for reduction of the eddy current loss.All of these enlighten applications of the wires.In this thesis,new techniques or mechanisms such as electroplasticity and deformation twinning were employed to further improve the formability of the Fe-6.5wt.%Si alloy,besides the previous techniques like decreasing the ordering and controlling the shape and size of the grains.Fabrication parameters of bars and wires were designed and optimized.The evolutions of microstructures.textures and ordered phases were investigated during bar rolling and drawing process.Mechanical properties and magnetic properties were also measured.The main researches are as follows:(1)Deformation mechanism in the bars with equiaxed grains at intermediate temperature during tensile tests was investigated.Effect of grain size,orientation,ordered phase and deformation twinning on the ductility of the Fe-6.5wt.%Si alloy was studied.The low degree of order and the strong<110>fiber texture rather than the grain size played more important roles in improving the plasticity.Both slip and twinning were the main deformation mechanism in the ?6mm bars with equiaxed grains at intermediate temperature.The orientation was adjustedl by twinning,which was beneficial to the activation of new dislocation slip,and the tensile ductility was enhanced by deformation twinning.(2)The flow behavior of the Fe-6.5wt.%Si alloys during hot compression was investigated.The activation energy(Q)and the constitutive equation were calculated.Processing maps were established.With the increase of the boron content,the value of Q decreased,which indicated that boron alloying improved the deformation ability.Based on the analyses of processing maps,surface quality,ordered structures,and microstructures,the optimized rolling parameters were the temperature and deformation rate of below 800? and 50%.(3)Parameters of bar rolling for this alloy were designed.Evolution of microstructures,textures and ordered phases were investigated during the bar rolling.?7.5mm bars were fabricated through three rolling stages:rough rolling,medium rolling,and finish rolling.During the bar rolling,the grain size decreased.Area fractions of the {100}<011>and {001}<100>oriented grains decreased to 0,whereas the {100}<001>,{011}<211>and {112}<110>components increased.Notably,y fiber with the {11}<110>component were dominant.Compared with the rotary swaged bars in the surface quality and the elongation,the bar rolling was the more appropriate technology to fabricate the Fe-6.5wt.%Si alloy bars.(4)Parameters of warm drawing for Fe-6.5wt.%Si alloy were optimized through adjusting the temperature,rolling speed,deformation rate and heat treatment.The evolutions of microstructures and textures were investigated.02mm wires with enhanced room-temperature ductility(above 5%)were fabricated.During the warm drawing.the equiaxed grains evolved into fibril-shaped vimineous grains,and the intensity of<110>fiber texture increased.Moreover,the intensity of {100}<001>firstly increased and then decreased.Furthermore,the intensity of {112}<111>and {111}<110>component increased gradually.(5)A device was set up for the electroplastic drawing.The parameters were designed and optimized.?1.0mm wires were prepared by electroplastic drawing.Evolutions of microstructures,textures and ordered phases were investigated,and the mechanical properties were measured.During the electroplastic drawing,grains were refined by plastic strain.The intensity of {100}<011>increased gradually,and the intensity of {011}<100>and {111}<211>firstly increased and then remained constant.Moreover,D03 ordered phase was suppressed,and the ordering degree were gradually reduced.(6)Magnetic properties of ?1.5mm Fe-6.5wt.%Si alloy wires after heat treatment were investigated.The value of B8 B25.B50.?m and Hc were 1.27T,1.41T,1.54T,27400 and 13.37A/m.respectively.Boron alloying was harmful for magnetic induction,maximum permeability,and coercive force.However,when the content of boron increased to 0.01%,the magnetic induction was slightly improved.Compared with the Fe-6.5wt.%Si alloy ribbons fabricated by cold rolling,melt spinning,and CVD method,the magnetic properties of the Fe-6.5wt.%Si alloy wires were better.Therefore,the Fe-6.5wt.%Si alloy wires were available.