Process Study On Semi Solid Slurries Prepared By Helical Curve Duct

In this paper,Helical Curve Duct(HCD)slurry preparation device is designed.The influence of the HCD device structure parameters and process parameters on the microstructure of the slurry was discussed,and the distribution uniformity of the primary phase was quantitatively calculated by the multifractal method;The microstructures of the samples prepared by HCD were reconstructed based on the continuous sectioning technique,and the basic information,the fractal dimension and the anisotropy of the three groups of representative samples were measured;The three-dimensional reconstructed slurry microstructures were resliced to obtain 9 sets of resliced series,And a series of 12 slices(9 sets of resliced series and 3 sets of original series)were calculated and the statistical analysis was carried out;The incision sections of the samples prepared by HCD were analyzed,and the typical incision sections were reconstructed and the multifractal calculation was made.The nonuniformity characteristics of the three-dimensional incision sections were characterized.The characteristics of crack propagation on the incision sections were obtained by image processing and quantitative analysis was performed by multifractal analysis.The influence of the microstructure on the section characteristics of the incision sections was analyzed from another perspective.Main research contents and results:The semi-solid slurry preparation of A356,7075 and 6063 aluminum alloy,AZ91 magnesium alloy and copper calcium alloy was realized by HCD experimental device.Based on A356 alloy and 7075 alloy,the influence of structural parameters and technological parameters on preparation of slurry was studied.The spiral angle of helical curve duct,pouring temperature and flow time will exert influence on the microstructures of prepared slurries,and the three groups of parameters are in a certain range of work.For A356,7075 and 6063 aluminum alloy,AZ91 magnesium alloy,the helical angle of the effective range is from 270 ° to 720 °.The flow time of the melt alloy in the duct between 4s and 11 s ensures that the alloy flows smoothly through the duct.In the range of effective flow time,the excellent alloy slurries were prepared with the reasonable relationship between the helix angle of HCD device and the pouring temperature of the experimental alloy.The range of pouring temperature for A356 alloy is from 630 to 640 oC,for 7075 alloy is from 640 to 665 oC.The pouring temperature for 6063 alloy should not exceed 665 oC,and the standing time after preparation slurry of 7075 and 6063 alloy is not more than 90 s,or it is difficult to control that the solid fraction produce rapid changes in a very short period of time.The effects of the helix angle(270 °,360 °,540 ° and 720 °)on the microstructure of A356 alloy slurries were investigated.The spectral width ?? was 0.9498,1.7277,0.8098 and 0.8196,respectively.The spectral width of 540° was the narrowest,and the microstructures of the slurries were the most homogeneous.The effects of pouring temperature(630,635,640 and 650°C)on the microstructure were investigated.The spectral width ?? was 1.6280,0.8596,1.2566 and 2.0878,respectively.The spectral width of 635 °C was the narrowest,and the distribution was the most uniform tissue;Study on the influence on the flow time,the difference between the spectral widths is very small.The influence on the uniformity of the microstructure caused by the alloy melt flow in the helical curve duct is far less than caused by the pouring temperature and helical angle.The multifractal calculation of the primary phases of 7075 and 6063 alloy were carried out,as A356 alloy,the effect of helix angle and pouring temperature on the microstructure of the slurry is very obvious,but the degree is different.All of these results can be reflected in the spectral width ??.All the multifractal spectra of the primary phase of the experimental alloy are left hook,and the probability subset is dominant.There is a different place,in the investigation of the spiral angle and pouring temperature on the impact of slurry microstructure,the spectral width ?? of A356 alloy is in the group of the smallest equivalent diameter,but of 7075 and 6063 alloy is in the group of the largest equivalent diameter,and most relatively uniform tissue distribution.The 240 slices of three typical tissue samples were obtained by manual polishing,and all metallographic features were extracted through Image Processing.Then three-dimensional reconstruction of slurry microstructure was performed in Image J,MIMICS and 3Ddoctor,respectively.Based on the reconstruction of the three groups of slurry microstructure,the measurement of the basic information,the fractal dimension of the primary phase and the degree of anisotropy were completed.The results show that fractal dimension of the primary phase of the three groups was 2.4657,2.5340 and 2.5850,respectively;and the linear correlation coefficients were 0.9961,0.9965 and 0.997,respectively.The degree of anisotropy was 0.295,0.1671 and 0.711,respectively.On the basis of the three-dimensional reconstruction of the slurry microstructure,three numerical models of the slurry structure were established.The equivalent diameter,Feret diameter and shape factor of sections(9 groups of resliced slices and 3 groups of original slices)were measured and the statistical analysis was carried out.The results show that the slicing measurement results of the resliced axial plane were the closest to those of the original slice layer.In the third group,the degree of anisotropy of the dendritic primary phase was the greatest.The maximum measurement deviation of the measurement results of the equivalent diameter,Feret diameter and shape factor between resliced and original slices is 32.81%,42.00% and 9.67%,respectively.The result,in turn,confirms the measurement of the degree of anisotropy in Chapter 4.In this proposition of the small degree of anisotropy of microstructure,the measurement of Feret diameter is the most reliable,of the shape factor in the next,and the last is of the equivalent diameter.The results show that the incision section of the HCD are similar to that of the remelted blank section,and the difference between the untreated section and the two mentioned above is very obvious.The distinguish among the four incision sections(untreated 595 oC and JL 590 oC,JL595oC and PL585oC)of A356 alloy slurries were investigated.The multifractal calculation results show that the spectral width ?? was 1.0310,0.7014,0.5799 and 0.4441,respectively.The ?? of untreated 595°C is the largest,and of the PL 585°C is the smallest.The results show that the spectral width ?? of the crack propagation is 1.3702,1.2325,0.8938,0.9619,respectively.and the distribution of crack propagation on the JL 595 oC incision section is the most uniform,then the PL 585 oC,Followed by the JL 590 oC incision section,and finally the untreated 595 oC incision section.The contour maps of the four typical incision sections can also support this calculation.