Microstructure and properties of unleaded free-cutting brass containing stibium

A new environmental friendly cutting brass containing stibium instead of lead was produced by casting and rolling. The microstructure was observed and the mechanical,dezincification and cutting properties were studied. The results show that the white particles distribute in both grains and grain boundaries,and the particles are mainly intermetallics containing stibium. The tensile strength,yield strength and elongation percentage of half-hard Sb-brass is 461.72 MPa,213.3 MPa and 15.67%,respectively. Corresponding to HPb59-1 by the size as well as appearance of the chips and the mechanism of free-cutting,the cutting property of unleaded free-cutting Sb-brass is excellent. The unleaded Sb-brass has excellent dezincification corrosion resistance,and the average depth of longitudinal section is about 295.4 μm,while the average depth of lateral section is about 214.7 μm,and it is feasible to develop a new unleaded free-cutting Sb-brass.

Preparation of lead-free free-cutting graphite brasses by graphitization of cementite

Graphite brasses were prepared by graphitizing annealing of cast brasses containing cementite particles,which were in-situ formed during the fasting process.The eutectic cast iron as carbon source was added into common brasses by casting.SEM and EDS were used to analyze the microstructure of graphite brasses,and the relationship between the microstructure and machinability was investigated.The results show that graphite particles are formed by the decomposition of cementite particles in cast brasses.The graphite particles are uniformly dispersed in the brass matrix with the average size of 5.0 μm and the volume fraction of ~1.1%.The machinability in the graphite brass is dramatically increased relative to the common brass,because of the lubricating properties of graphite particles and its role in chip breaking.The workpiece surface of the graphite brasses chips is smooth and burr-free,and the chips of graphite brasses are short（C-shape） and discontinuous,which is much better than that of the long spiral chips of common brasses.

Simulation of the continuous casting process in a mold of free-cutting steel 38MnVS based on a MiLE method

A new method called mixed Lagrangian and Eulerian （MiLE） method was used to simulate the continuous casting process in a mold of free-cutting steel 38MnVS.The simulation results are basically in agreement with experimental data in the literature,achieving the three-dimensional visualization of temperature distribution,melt flow,shell thickness,and stress distribution of blooms in a mold.It is shown that the flow velocity of steel melt becomes smaller gradually as the casting proceeds.When the flow reaches a certain depth,two types of flow patterns can be observed in the upper zone of the mold.The first flow pattern is to flow downwards,and the second one is to flow upwards to the meniscus.The corner temperature is higher,and the thickness is thinner than those in the mid-face.The effective stress in the corner area is much bigger than that in the mid-face,indicating that the corner area is the dangerous zone of cracking.

FRACTAL GEOMETRY STUDY OF CORRELATION BETWEEN IMPACT TOUGHNESS OF STEEL AND PARAMETERS OF FREE-CUTTING PHASE

Studies were made of the calculation of fractal dimension of transverse impact fracture sur- face,and of the correlation between impact toughness of steel and parameters of free-cutting phase by means of the developed fractal geometry model of crack propagation.It is believed that the area fraction,f,of free-cutting phase is negligibly influential to the longitudinal im- pact toughness,as f1 .While the aspect ratio,saying ratio of length to width,of free-cut. ting phase is inversely influential to the transverse impact toughness.This may .be the reason why the transverse impact toughness of free-cutting steel containing more rare earth contrast to sulphur is even higher than the low sulphur containing steel.

Experimental Study and Thermodynamical Calculation on the Formation of Eutectic Phase of MnS-RE_2S_3 and(Mn,Ca)S-RE_2S_3 in Sulfur-Containing Free-Cutting Steel

The free-cutting phase in RE or Ca-RE treated sulfur-containing free-cutting steel is the eutectic phases of MnS-RE_2S_3 and (Mn,Ca)S-RE_2S_3,respectively.The atomic ratio of RE/S needed to modify all the MnS into the eutectic phase is higher than 1.48 or 1.41-1.37 Ca/S,when RE or Ca-RE is used as the modifiz- er in the sulfur-containing free-cutting steel.Moreover,the thermodynamical calculation shows that the eutectic temperature is lower than the solidifying temperature,which is the key condition for the eutectic phase to keep globual during solidifying.

Influence of Ca/S and Rolling Reduction on Shape of Sulphide in Free-cutting Steel 5NiSCa

1.IntroductionThe shape of sulphide has a great influ-ence on machinability and transverse prop-erty of steel.It is very important to obtainoval sulphide instead of elongated one forimproving machinability and transverseproperties[1,2].

A free-cutting and ductile CuAlMnZnTiB shape memory alloy

The mechanical properties and cutting performance of the designed Cu Al Mn Zn Ti B shape memory alloy were studied by tensile test and microstructure observation. Using X-ray diffractometry, differential scanning calorimetry(DSC) and semi-quantitative shape memory effect test, the microstructure and shape memory effect were analyzed. It is found that lots of βphase and few α phase are formed in the quenching of Cu-7.5Al-9.7Mn-3.4Zn-0.3Ti-0.14B(mass fraction, %) alloy, a great deal of martensite and few α phase are formed in the aging alloy, while the annealing alloy is composed of a great deal of α phase and few βphase. The tensile strength and elongation of the annealed alloy are 649 MPa and 17.1%, respectively. Some tiny and dispersion distributed second phase particles are generated in Ti and B precipitates, greatly improving the alloy machinability.

Effect of Annealing Atmosphere on the Mechanical Property of Free-cutting Phosphor Bronze Alloy

The present work is focused on the influence of annealing atmosphere on the microstructure and mechanical property of free-cutting phosphor bronze alloy.The annealing of the alloy was conducted in the three kinds of annealing atmosphere such as air,vacuum and nitrogen.After annealing,a discernable difference in recystallized grain size and lead particle size was not appeared with different annealing atmosphere.The tensile strength of the alloy annealed in air or nitrogen atmosphere was higher than that of those annealed in vacuum atmosphere.In thecase of the alloy annealed in vacuum atmosphere,the mechanical strength was reduced by vaporization of zinc.In the case of annealing in nitrogen and in air atmosphere,the sweating of lead was occurred.However,the inverse segregation of lead was suppressed by copper oxide layer on the surface annealed in air.This copper oxide layer leads to a decrease of the yield during fabrication process. Therefore,annealing of the alloy in nitrogen atmosphere is favorable in terms of the mechanical strength and yield.

Influence of cold deformation on microstructure,mechanical properties,and corrosion resistance of high-sulfur free-cutting 316LS stainless steel

In this study,the influence of plastic deformation produced by cold rolling at reduction ratios ranging from 10% to 80% on the microstructure,mechanical properties,and pitting corrosion behavior of high-sulfur freecutting 316 LS austenitic stainless steel was investigated. The results indicate that slipping is the predominant effect and that sulfide inclusions extend along the rolling direction during the cold deformation of 316 LS. The strong austenite stability of 316 LS results in the formation of only a small quantity of deformation-induced martensite. The experimental results reveal that the strength,hardness,and yield ratio increased with increases in the reduction ratio,mainly due to work hardening,whereas the elongation decreased drastically,due to the combined effect of the work hardening and brittleness caused by the numerous sulfide inclusions. Electrochemically active sites on the surface of316 LS increased with an increased reduction ratio,which caused an increased current fluctuation in the passive zone. This also caused the breakdown potential（ E_b） near the pitting zone to exhibit a gradual increase in the zigzag current shift to the left on the polarization curves. The E_b of 316 LS decreased with increases in the reduction ratio,mainly due to the extended sulfide inclusions,the increased dislocation density,and the deformation-induced martensite content.

Inhibition mechanism of air nanobubbles on brass corrosion in circulating cooling water systems

Air nanobubbles(A-NBs)were used to inhibit the brass corrosion in circulating cooling water for the first time in the study.The results of mass loss method and electrochemical method showed that A-NBs had the obvious corrosion inhibition effect.The inhibition rate reached 52%at 35℃.The impedance and surface characterization results of corrosion samples indicated that the corrosion inhibition mechanisms of A-NBs mainly included adsorption of corrosion ions,promoting the formation of the passivation film on metal surface and the formation of the bubble layer and scale film on metal surface.A-NBs are potential excellent corrosion inhibitors.

黄铜集流体在无负极锂金属电池中的应用研究

虽然无负极锂金属电池(AF-LMBs)具有能量密度高、结构简单等优势,但是金属锂在负极集流体界面不可逆的沉积/剥离过程以及与电解液之间的副反应会大量消耗电池中有限的活性锂,导致电池容量迅速衰减。开发高性能的负极集流体是提升AF-LMBs循环寿命的有效策略之一。因此,本文研究了商业黄铜箔(F-Cu-Zn)作为负极集流体在AF-LMBs中的电化学性能,并且结合多种表征技术揭示了F-Cu-Zn电极在循环过程中的结构演变。结果表明:与商业铜箔(F-Cu)相比,F-Cu-Zn含有丰富的亲锂位点,诱导金属锂均匀成核与生长,所组装的Cu-Zn||NCM712软包全电池的室温循环寿命从75次增加至117次。此外,F-Cu-Zn电极中的Zn元素会在循环过程中不断溶解,最终在电极表层形成三维多孔结构。

Sensitivity of springback and section deformation to process parameters in rotary draw bending of thin-walled rectangular H96 brass tube

In order to study the effects of the process parameters on springback and section deformation, a sensitivity analysis model was established based on the combination use of the multi-parameter sensitivity analysis method and the springback/section deformation prediction finite element model, and by using this model the sensitivities of the springback and the section deformation to process parameters were analyzed and compared. The results show that the most sensitive process conditions for springback angle are the boost speed and the pressure of pressure die, and the most sensitive process condition for section deformation is the number of cores. When the clamp force, the boost speed and the pressure of pressure die are utilized to control section deformation, the effect of these process parameters on springback should be considered. When the process parameters are mainly used to control springback, the effect of these process parameters on the section deformation should be always considered.

采用二氧化氯消毒水时添加咪唑基离子液体对黄铜缓蚀作用的研究

[目的]采用二氧化氯(ClO_(2))对水进行消毒时常常面临黄铜件腐蚀问题,寻找适宜的缓蚀剂具有重要意义。[方法]通过静态挂片试验、动电位极化曲线测试、腐蚀形貌观察及产物成分分析,研究了在ClO_(2)溶液中添加1-丁基-3-甲基咪唑乙酸盐(BMIMAc)或1-丁基-3-甲基咪唑溴盐(BMIMBr)对H62黄铜的缓蚀效果,并通过密度泛函理论(DFT)计算及分子动力学(MD)模拟探讨了两种咪唑基离子液体对黄铜的缓蚀机理。[结果]在ClO_(2)溶液中添加BMIMAc或BMIMBr都能够在一定程度上抑制黄铜的腐蚀,并且缓蚀效率随着BMIMAc或BMIMBr浓度的增大而升高,BMIMAc的缓蚀效果优于BMIMBr。BMIMAc和BMIMBr都属于抑制阴极反应的阴极缓蚀剂,二者在黄铜表面的吸附都遵循Langmuir等温模型。BMIMAc和BMIMBr都能够以平行排列的方式吸附在黄铜表面,生成阻止黄铜与腐蚀溶液接触的吸附膜,从而减缓腐蚀。[结论]在采用ClO_(2)消毒水的过程中添加适量BMIMAc或BMIMBr都能够对黄铜起到有效的缓蚀作用。

薄壁H65黄铜管高频感应焊接接头组织和力学性能

对薄壁H65黄铜高频感应焊接后的焊接接头微观组织和力学性能进行了研究。结果表明,利用高频感应焊接技术焊接H65黄铜管,获得了表面成型良好的焊接接头,实现了高质量焊接。焊接接头熔合区和热影响区均呈上下宽,中间窄的腰鼓状,焊接接头宽度约为173μm,其中熔合区宽约15μm,由大量细小的等轴状晶粒和少量条状晶粒组成,熔合区和热影响区的晶粒较母材得到细化。焊接接头抗拉强度为400 MPa,达到母材抗拉强度的97.6%,这是由于在拉伸变形过程中,晶粒的细化阻碍位错变形,且各晶粒间的位向差使位错相互交割,提高了焊接接头的强度,焊接接头断裂发生在热影响区,为韧性断裂,这是焊接过程中挤压辊的加工硬化与焊后退火软化共同作用影响热影响区力学性能所致。焊接接头显微硬度呈现“ʌ”形分布,熔合区平均硬度值为145HV,热影响区137HV,母材129HV,熔合区硬度较母材提高了16%,焊接时产生的加工硬化使熔合区强度得到提升。

铜及黄铜与模具钢界面稳态接触换热行为的研究

接触换热系数直接决定金属热加工过程的温度分布,进而影响零件的微观组织及使役性能。本文采用自主开发的稳态接触换热设备和测量系统,系统研究了纯铜及H62黄铜与H13模具钢在接触面温度为200~600℃、压力为1.56~12.56 MPa下的接触换热行为。结果表明,载荷加载的历程对接触换热系数有较大影响,相比于从低载荷加载到目标压力时,从高载荷卸载到同一目标压力测得的接触换热系数更高;在相同加载历程下,接触换热系数随着界面温差的升高而增加,且界面温度高于400℃时接触换热系数增速变快;接触换热系数与压力呈幂指数关系增长,随着压力的增大,接触换热系数增长逐渐变得缓慢;在相同条件下,黄铜/H13传热时的温度梯度更大,导致黄铜/H13的接触换热系数更大。

超薄壁黄铜散热器扁管高频感应焊接接头的组织和性能

采用高频感应焊接技术对0.13 mm壁厚的H65黄铜扁管进行焊接,利用光学显微镜、扫描电镜、电子探针、电子背散射衍射、显微硬度仪以及拉伸实验对焊接接头的微观组织和力学性能进行了研究。结果表明:高频感应焊接H65黄铜扁管的焊接接头无裂纹、气孔等缺陷,焊缝区没有出现Zn的大量蒸发。焊接接头的抗拉强度达到400 MPa,达到母材的94%,伸长率为33.89%,与母材接近;焊接接头的显微硬度呈W型分布,熔合区最高,母材区次之,热影响区最小。焊接过程的挤压作用导致焊缝位错密度增加,产生加工硬化,是影响焊接接头硬度分布的主要原因;与母材相比,焊接接头的显微组织得到明显的细化,平均晶粒尺寸为1μm,是母材的50%,小角度晶界增加到了72%,大角度晶界下降到了28%,其中孪晶界下降到2%,进一步提高了焊接接头的力学性能。

熔体过热和脉冲磁场协同处理对Mn_(5)Si_(3)增强Cu-35Zn-3Al合金显微组织、力学和耐磨性能的影响

研究熔体过热和脉冲磁场协同处理对Mn_(5)Si_(3)增强Cu-35Zn-3Al合金显微组织、力学和耐磨性能的影响。研究结果表明,协同处理促进了熔体中的溶质迁移以及Mn_(5)Si_(3)晶体生长的吸附动力学,抑制了六棱柱形貌Mn_(5)Si_(3)颗粒上孔洞的形成。协同处理后热锻态合金的抗拉强度和伸长率分别提高了9.0%和66.5%,这是由于拉伸变形过程中不含孔洞的Mn_(5)Si_(3)颗粒断裂强度提高,产生的应力集中减小,因此失效方式由脆性解理断裂转变为从基体中拔出,颗粒和基体间的载荷传递作用增强。在承受摩擦时,协同处理后合金的磨损亚表层中Mn_(5)Si_(3)颗粒不易发生剪切断裂,抑制了裂纹扩展和材料剥落,因而产生的剥层磨损减小,合金耐磨性显著提高。

渗碳体石墨化制备无铅石墨黄铜的腐蚀性能

以共晶铸铁作为碳源,通过熔铸及渗碳体石墨化工艺制备不同石墨含量的石墨黄铜。对石墨黄铜进行脱锌腐蚀试验,通过SEM和EDS分析了石墨黄铜的腐蚀组织、腐蚀性能和石墨含量的关系,并探讨了石墨黄铜的腐蚀机理。结果表明:随着铸铁添加量的增加,石墨黄铜的耐腐蚀性先提高后降低,铸铁添加量为5%时,石墨黄铜的腐蚀产物会在合金表面形成一层完整氧化膜,腐蚀面基本没有裂纹和孔洞,脱锌层厚度最小,平均为144μm,其耐腐蚀性最好。石墨黄铜的耐腐蚀性能由其组织、成分及石墨颗粒的分布状态共同作用而成。

铜丝结扎法治疗下颌第二恒磨牙异位萌出1例

第二恒磨牙异位萌出若未得到及时治疗,会导致相邻的第一磨牙牙体组织吸收、牙齿早失、咀嚼效率下降及其他严重的错𬌗畸形。及时发现和处理第二恒磨牙异位萌出,对预防青少年错𬌗畸形、建立正常咬合关系具有重要的意义。然而,目前针对下颌第二恒磨牙异位萌出的病例报告比较少见,大多治疗方法主要为手术及正畸的方式,且缺乏长期的随访。本文报道1例采用铜丝结扎法治疗下颌第二恒磨牙异位萌出,使恒牙顺利萌出并建立正常咬合。术后观察5年,咬合稳定,牙根发育、牙髓活力及牙周状况正常。本文为近中倾斜度不大且已经部分萌出的阻生年轻下颌第二恒磨牙提供一种治疗周期短、简便及微创的临床思路。

基于自由定标激光诱导击穿光谱的黄铜定量研究

为了实现黄铜样品中铜、锌元素质量分数的快速定量检测,采用自由定标激光诱导击穿光谱技术(CF-LIBS)对3种黄铜样品开展了相关研究。分别选择铜元素的6条、锌元素的4条特征谱线为分析对象,在单次脉冲和10次脉冲平均光谱采集方式下,对比分析铜和锌元素特征谱线的相对标准偏差(RSD)。结果表明,与单次脉冲相比,10次脉冲平均使铜和锌的光谱RSD平均值分别下降8.8%和12.3%;采用CF-LIBS对3种黄铜样品中铜、锌元素质量分数进行定量计算,铜、锌元素的温度与等离子体温度平均值之间的相对误差分别为5.2%、0.9%和7.1%;3种样品中铜元素质量分数的相对误差分别为5.6%、0.5%和1.6%,锌元素质量分数的相对误差分别为9.2%、2.0%和13.3%。CF-LIBS有望为黄铜元素质量分数的快速及精准检测提供方法支持,为进一步实现研制合金样品元素质量分数便携式检测设备提供数据和技术支持。