The Effect Of Ultra-low Temperature Rolling And Ni,Si Elements Addition On The Microstructures And Properties Of Brass

Brass strip is one of the most important basic materials and is widely used in various fields of industry and national economy.Although the preparation process of traditional brass strips is very mature in our country,the high-performance brass strips with good mechanical properties and electrical conductivity and corresponding preparation process are still valuable to be researched and explored.Firstly,the effect of ultra-low temperature rolling and annealing on the microstructure and properties of H65 brass is systematically researched in the present study.Secondly,the precipitation strengthening nickel-silicon brass is developed to solve the strength decreasing of ultra-low temperature rolling sample caused by annealing.Then obtaining nickel silicon brass strip with excellent comprehensive performance through ultra-low temperature rolling and aging treatment.Then the high-strength and good ductility Cu-30Zn alloy strip with low deformation amount is prepared by ultra-low temperature rolling.At the same time,high-performance Cu-30Zn-1Ni-0.2Si alloy strip is prepared through ultra-low temperature rolling and combined with annealing treatment.The ultra-low temperature rolling and precipitation strengthening nickel-silicon brass developed in the present study provide new ideas and feasible technical reference for the research and development of brass strips in our country.The main research results obtained are listed as follows:(1)H65 brass strip was subjected to room temperature rolling and ultra-low temperature rolling with diferent deformation amount,the advantages and disadvantages of ultra-low temperature rolling on the microstructure and propertiesof H65 brass strips was studied.The strengthening and toughening mechanism of 90%deformation ultra-low temperature rolling sample were revealed.With the increase of deformation amount,ultra-low temperature rolling is more obvious to promote the grain refinement,dislocation accumulation and deformation twin generation of H65 brass strip compared with room temperature rolling.When the deformation amount is 90%,the microstructure of ultra-low-temperature rolling sample shows ultra-fine grain characteristics,the average grain size is 0.1 ?m,and there are large number of nano-scale deformation twins and serious dislocation accumulation.The tensile strength of 90%deformation ultra-low temperature rolling sample is significantly higher than that of 90%deformation room temperature rolling sample caused by the combined effect of fine-grain strengthening,dislocation strengthening and twin strengthening mechanisms,which are 835.3MPa and 718.5MPa,respectively.Moreover,due to the existence of large number of nano-scale deformation twins,the elongation of the ultra-low temperaure rolling sample is equivalent to that of the room temperature rolling sample,which are 2.9%and 3.1%,respectively.(2)The variationins of microstructure and properties of 90%deformation H65 brass samples during the annealing treatment at 300? were systematically studied.Compared with the room temperature rolling sample,the recovery and recrystallization behavior of the ultra-low temperature rolled sample during the annealing process is more rapid and obvious.After 1h annealing treatment,the dislocation density of ultra-low temperature rolling sample drops from 15.87×10¹³m^-2 to 8.04×10¹³n-2,and the average grain size increased form 0.1?m to 0.64pm.However,the dislocation density of room temperature rolling sample decreased to 7.15×10¹³m^-2,and the average grain size increased from 0.53?m to 1.72?m.Meanwhile,the elongation and electrical conductivity of ultra-low temperature rolling sample significantly improve to 12.3%and 11.2%IACS(the elongation and electrical conductivity of the as-rolled sample are 2.7%and 7.6%IACS,respectively).The elongation and conductivity of room temperature rolling sample are 8.2%and 13.6%IACS,respectively(the elongation and conductivity of the as-rolled sample are 2.9%and 11.4%IACS,respectively).However,the tensile strength of ultra-low temperature rolling sample decreases from 835.3MPa to 752.7MPa,but it was significantly higher than that of room temperature rollin sample(673.5MPa).(3)Based on the Cu-35Zn alloy,three kinds of nickel-silicon brass(NSB-1,NSB-2 and NSB-3 brass respectively)were prepared.And the solidification microstructure and the micorstructure and properties after solution and aging treatment were systematically studied.It is found that nickel and silicon elements exist as two forms:solid solution atoms and?-Ni₂Si phase.In NSB-1 brass,the ?-Ni₂Si phase is mainly distributed at the grain boundary and the size is relatively small.In NSB-2 and NSB-3 brass,the ?-Ni₂Si phase is distributed both in the grain boundary and grain,and the size is relatively large.Three kinds of nickel-silicon brass were solid-solution treated at 750?,and it was found that the ?-Ni₂Si phase in NSB-1 and NSB-2 brass can be completely dissolved into the matrix.But the ?-Ni₂Si phase cannot be completely dissolved into the matrix in NSB-3 brass.The single-phase supersaturated solid solutions of NSB-1 and NSB-2 were aged at 300?.With the extension of aging time,?-Ni₂Si precipitates were generated in these two alloys,and NSB-2 can generat more ?-Ni₂Si precipitates.During the aging treatment,the electrical conductivity and hardness of NSB-1 and NSB-2 brass increases,it is more obvious for NSB-2 brass.After 4h of aging treatment,the conductivity of NSB-1 and NSB-2 brass increase to 16.1%IACS and 15.9%IACS,respectively,and the hardness of increased to 158.2HV and 183.4HV(4)The effect of 90%deformation ultra-low temperature rolling on the precipitation behavior of ?-Ni₂Si phase during aging treatment were studied,and the change of properties caused by ?-Ni₂Si phase was also researched.Before aging treatment,the single-phase supersaturated solid solution of NSB-2 brass was subjected to room temperature rolling and ultra-low temperature rolling with 90%deformation,and then aging treatment was performed at 300?.It is found that compared with room temperature rolling,due to the introduction of large number of dislocations,grain boundaries and other defects in the ultra-low temperature rolling sample,it has a more obvious promotion effect on the precipitation behavior of the?-Ni₂Si phase,which in turn has a more significant impact on the properties.After aged for 3h,the room temperature rolling sample has a large amount of ?-Ni₂Si phase.Meanwhile,the strength,elongation and conductivity are 735.1MPa,17.8%and 14.9%IACS,respectively.However,the ultra-low temperature rolling sample generats large number of small and dispersed ?-Ni₂Si precipitates after aged 2h,then the strength,elongation and conductivity are 769.8MPa,18.4%and 14.8%IACS,respectively.(5)Cu-30Zn alloy was subjected to ultra-low temperature rolling with 50%,70%and 90%deformation amount,the microstructure and properties were analyzed and researched.Compared with the 90%deformation room temperature rolling sample,there are large number of ultra-fine grains and nano-scale deformation twins in the 70%deformation ultra-low temperature rolling sample.Meanwhile,the strength(695.4MPa)and elongation(7.2%)of the 70%deformation ultra-low temperature rolling sample are both higher than those of the 90%deformation room temperature rolling sample(strength and elongation are 641.7MPa and 3.7%,respectively).The solid solution Cu-30Zn-1Ni-0.2Si alloy was subjected to ultra-low temperature rolling with 90%deformation amount and annealed at 300? to study the changes of its microstructure and properties.It is found that large number of fine-sized?-Ni₂Si precipitates generate after annealed for 1h.At the same time,the strength,elongation,and conductivity are 768.4MPa,12.1%,and 15.3%IACS.