Rolling Experiment Of Ultra Thin Metal Strip And Its Size Effect

With wide application of micro electric mechanical systems(MEMS)on aerospace,precision instrument,biological and medical et al,and the demand of quantity and quality of metal ultra thin strip increased year by year.However,the mechanical properties of metal ultra thin strip are different from the macroscale.That difference could have an impact on the manufacturing process,quality control and Stability.On the basis of background and reasons,we have developed the low cost techniques for asymmetrical rolling ultra thin strip without intermediate annealing,which funded by the National Nature Science Foundation of China.The effect of process parameters including rolling speed ratio on rolling pressure and cross shear ratio were analyzed by ABAQUS software.Taking commercial pure aluminium AA1060,commercial pure copper T2 and low carbon steel Q195 as research objects used widely,that was mainly studied on the size effect in rolling process,and explored to the microstructure transformation and deformation characters.On that basis,single layer grain ultra thin strip,which only one layer grain in thickness direction were prepared by proper heat treatment,furthermore,the mechanical properties of single layer grain ultra-thin strip were investigated.The chief of original work and results are as follows:(1)The reasons of shape defects have been analyzed,and the corresponding strategies and resolutions were preferred also,combined rolling experimental of ultra-thin strip in laboratory.The 2D elastic plastic FEM model to simulate the ultra-thin strip rolling process were developed,the errors between optimization values and theoretic results of the exit thickness and rolling force were 3.7%and 7.3%respectively,it was shown that these models had high precision and authenticity.The effect of rolling conditions including rolling speed ratio,friction coefficient,forward-backward tension,preloading force and deformation resistance of raw materials on distribution of rolling pressure,contact arc length and cross shear ratio were discussed.Experiment results shown that rolling pressure and contact arc length decreased as cross shear ratio and tensile stress increasing,and increased as friction coefficient,preloading force and deformation resistance of raw materials increasing.The cross shear ratio increased as rolling speed ratio,friction coefficient,forward tension and preloading force increasing,and decreased as backward tension increasing.Besides,cross shear ratio decreased slightly as deformation resistance of raw materials increasing.(2)Based on the research of the effect of process parameters on asymmetrical rolling ultra thin strip process,AA1060 ultra thin strip with thickness of 0.3?0.02 mm,which initial thickness were 8 mm,4 mm and 2 mm respectively and mechanical properties were almost same,was prepared by asymmetrical rolling without intermediate annealing.Mechanical properties and microstructure of AA1060 ultra-thin strip were investigated in the rolling process.It was found that the size effect,which was the ultimate strength increased first and then decreased in rolling process,when true strain was more than 2.77,and thickness were 0.125 mm?0.1 mm.Asymmetrical rolling could effectively refined the grain size from-60?m to?500 nm,which mainly are high angle grain boundaries.In AA1060 aluminium ultra thin strip rolling process,the deform textures C-{112}<111>and B-{011}<211>increase gradually,and reach to maximum value at 0.1 mm thickness,then decrease significantly at 0.02 mm thickness and formed RC-{100}<011>.(3)T2 ultra-thin strip with thickness of 0.3?0.025 mm,which initial thickness were 5.80 mm,was prepared by asymmetrical rolling without intermediate annealing.Mechanical properties and microstructure of commercial pure copper T2 were investigated in the rolling process.The ultimate strength first increased from 5.8 mm to 0.1 mm;however,it decreased from 0.076 mm to 0.025 mm.It was found that grain sizes were refined from?60 ?m to?120 nm with high angle boundaries.As same as the ultimate strength,the dislocation density and micro strain increased first then decreased.The rolling textures consisted of copper C-{112}<111>,Brass Bs-{011}<211>,and S-{123}<634>.The texture intensity increased monotonously.(4)Q195 ultra-thin strip with thickness of 0.1?0.02 mm,which initial thickness were 0.3 mm,was prepared by asymmetrical rolling without intermediate annealing.Mechanical properties and microstructure of commercial pure copper Q195 were studied in the rolling process.It was found that the size effect on the ultimate strength with thickness changing.The tendence of micro hardness was same as the ultimate strength,increased first then decreased.The original microstructure was?10 ?m which was fibrous microstructures as increasing stain,and the grain boundaries were difficult to distinguish at thickness of 0.025 mm.(5)Combined the asymmetrical rolling compound forming with pull,press and shear and heat treatment,it was prepared of single layer grain ultra-thin strip with only one layer grain in thickness direction.Ten kinds of different T/D(Thickness/Grain size)sample were prepared by different annealing treatment(T/D=0.4-4.2).The ultimate strength was decreased notably as decreased T/D,which value was 3.6?2.0.The lower ultimate strength of single layer grain was due to the more free surfaces for dislocation escape in deformation process.(6)Size effect was been classified by mechanical principles in ultra-thin strip rolling process.The first order size effect,which rolling process of common metal materials was not interrupted by shape defects induced by work hardening as continue cold rolling without intermediate annealing,were related to the negative-roll-gap rolling in ultra-thin strip rolling.In the above condition,the edge cracks were been decreased by transverse stress.Moreover,the hydrostatic pressures were increased with the decreasing of thickness of sample,that was effectively restrained the formation and evolution.Therefore,the plasticity of sample was improved.The second order size effect,which ultimate strength increased first and then decreased,was related to the surface model.For commercial pure copper T2,the grain sizes was kept unchanged at?120 nm,when thicknesses were down from 0.076 mm to 0.025 mm,that increased the ratio of surface grains,and less constrict to dislocations,which led to the size effect of ultimate strength.