Evaluation of Mechanical and Microstructural Properties of <i>α</i>-Brass Alloy Produced from Scrap Copper and Zinc Metal through Sand Casting Process

Cu-Zn alloy (Brass) is widely used as an industrial material because of its excellent characteristics such as high corrosion resistance, non-magnetism and good forging ability. This paper evaluates the mechanical and microstructure properties of α-brass alloy gotten from scrap copper and zinc metal, and compares the properties with normal α-brass billets. Five different compositions of the α-brass alloy (Cu-5%Zn, Cu-10%Zn, Cu-15%Zn, Cu-20%Zn, Cu-30%Zn) were produced from scraps of copper wire and zinc batteries casing respectively by method of sand casting. The parts of the cast rods were machined to a specification of 60 mm × 100 mm × 300 mm on a lathe to obtain tensile test specimens. After homogenization annealing, the samples were heated in an electric furnace at 500℃ for 3 hours. The samples were etched with ferric chloride solution for 20 seconds and sent for metallographic examination. The result of the hardness test shows variation in hardness of the cast Cu-Zn alloys with increasing zinc content. The ductility and elongation of the α-brass decrease with increasing zinc content. The colouration of the α-brass changed from red to yellow as the zinc content increases. In conclusion, hard brass can be obtained from recycled Cu and Zn as compared to normal brass billets.

Study on typical hole defects in AZ91D magnesium alloy prepared by low pressure lost foam casting

The hole defects can easily occur in magnesium alloy castings that are prepared by low pressure lost foam casting(LP-LFC)process when the process parameters such as vacuum,pouring temperature and f illing velocity are not properly selected.In this study,the forming mechanism of the hole defects in AZ91D magnesium castings by LP-LFC process was investigated.The shape,location and surface appearance of the hole defects were observed using optical microscopy and scanning electron microscopy,and the chemical composition on the surface of the holes was analyzed using energy spectrometer.The result indicates that there are two types of hole defects,i.e.,the pyrolysis products related hole defects,including concentrative hole and blow hole defects,and slag related hole defects.The concentrative hole and the blow-hole defects were formed either by the liquidEPS degradation products entrapped in the molten metal under the condition that the pouring temperature is equal to or lower than 730℃,or by the hindered transport of EPS pyrolysis products.Some irregular shape hole defects were caused by slag or by coating slough entrapment when the pouring temperature is equal to 750℃and the f illing velocity is equal to or greater than 100 mm·s-1.To reduce or eliminate the hole defects,the vacuum and f illing velocity must be properly chosen to ensure that the metal front prof ile exhibits convex shape and in laminar current state,and the pouring temperature should be just high enough to ensure that the molten melt has adequate heat energy to complete the foam pyrolysis and to fully occupy the mould.For AZ91D magnesium castings in this study,the parameters should be 730℃pouring temperature,0.02-0.03 MPa vacuum and 80mm·s-1f illing velocity.

Process Optimization for AZ91 Mg-alloy Low-pressure EPC Process

The influence of a key process variable on the mold filling characteristics of AZ91 Mg-alloy was studied in the low pressure EPC process.The applied flow quantity of insert gas from 1 to 5 m~3/h associated with the pressurizing rate in the low pressure EPC casting process was considered for rectangle and L-shape plate casting. The experimental results show that there is an optimal flow quantity of insert gas for good mold filling characteristics in AZ91 Mg-alloy low-pressure EPC process. The optimal flow quantity of insert gas for the specimens is 3 to 4 m~3/h. Either less or higher than the optimal flow quantity of insert gas would lead to misrun defects or folds, blisters and porosity defects. The practice of hub casting confirmed that the low-pressure EPC process with an optimal processing variable exemplified as 4 m~3/h gas flow quantity was capable of producing complicated magnesium castings without misrun defects.

Principles and practice of low pressure-expendable pattern casting process for magnesium alloys

A newly developed low-pressure expendable pattern casting (LP-EPC) process was introduced and its basic principles or effect factors were further analyzed. According to theoretical calculation and experimental results, the major casting parameters that are of great and critical importance on the process include pressure and flux of filling gas, decomposition characteristic and density of foam pattern, thickness and permeability of coating, pouring temperature, vacuum degree and their combination. Most of casting defects can be effectively avoided by choosing the suitable parameters. The success achieved in pouring motor housing and exhaust manifold castings demonstrates the advantages of LP-EPC process in the production of high-complicated castings with high dimension accuracy.

Effect of lanthanum addition on microstructure and hardness of brass alloys produced by rheological squeeze casting

The effect of La addition(0-0.30 wt%)on the microstructure and hardness of rheological squeeze casting brass alloys was experimentally investigated.The rheological squeeze casting process is improved by controlling the wall surface crystals and melt flow rate to realise the preparation of semi-solid melt with flow,and a brass alloy workpiece with La is produced.The microstructure and properties of the brass alloy samples were investigated using metallography,scanning electron microscopy,energy-dispersive X-ray spectroscopy,X-ray diffraction and hardness testing.The results indicate that the hardness of the rheological squeeze casting brass alloy is increased by 20.4%from 108 to 130 HBW with an increase in the La content from 0 to 0.30 wt%.The micro structural analysis results show that La significantly refines the primary a-phase grains,and the main mechanism is the constitutional undercooling and heterogeneous nucleation caused by the La enrichment in the front of the solid-liquid interface.The squeeze pressure promotes undercooling,which improves the nucleation rate and affects the solute diffusion and nucleus growth.The dual effects of these two aspects aggravate the grain refinement process,consequently increasing the number of grain boundaries and improving the hardness of the brass alloy.

RB-1型铜合金铸造添加剂对HPb59-1黄铜组织的影响

研制了一种新型的铜合金铸造细化变质剂 (RB - 1) ,通过试验考察了它在HPb5 9- 1黄铜中的作用 .添加剂显著地细化了该合金的组织 ,消除了宏观柱状晶 ,同时增大了组织中α相的相对含量 ,并改善了其形态 ,提高了其分布均匀性 .RB - 1的添加量 (重量百分数 )在小于 0 .4%的范围内细化效果显著 ,而大于 1%时细化作用消失 ,重新出现柱状晶 .

稀土和硼细化处理对铸造铅黄铜组织和脱锌腐蚀性能的影响

研究了加入稀土和硼细化处理对铸造铅黄铜组织和脱锌腐蚀性能的影响。结果表明,加入稀土和硼后明显地细化了铸造铅黄铜的组织,使粗大的α、β板条状组织变成短小的片状或等轴状组织。用硼处理的组织细化效果要好于用稀土处理的效果,同时可以减轻铸造黄铜的脱锌腐蚀倾向。细化处理后壳杯试样的表面由未细化的粗糙表面变为光滑表面,结晶面组织由柱状晶变为等轴晶。加入细化剂可以明显改善黄铜抗脱锌腐蚀性能。

金属型铸造黄铜水嘴体工艺的研究

详细探讨了金属型铸造CE30型黄铜水嘴体的铸造工艺 ,着重试验了浇注系统和浇注位置对铸件质量的影响。试验结果表明 ,采用底注、封闭 开放式浇注系统可以有效地减少铸件中夹杂的数量 ,从而显著地提高水嘴的质量和合格率 ;试验结果还表明 ,在特定的条件下 ,铸件的重要面在浇注时不必要求其位于铸型底部。

电磁场对铅黄铜水平连铸坯组织及偏析的影响

研究了铅黄铜在无磁场、低频交变电磁场下水平连铸得到的铸坯横截面宏观组织、微观组织形貌及合金元素Pb的分布,并对其机理进行了分析。试验结果表明,在铅黄铜水平连铸的过程中施加低频交变电磁场能有效地细化晶粒及影响合金元素在横截面上的分布,并且电磁场有效地抑制了在常规水平连铸过程中出现的铸坯横截面上中下部位组织分布不均匀的现象。表现在铸坯横截面的凝固组织由上方主要为细小柱状晶、下方为粗大柱状晶变为均为细小的等轴晶,铸锭上部凝固滞后的现象消除;合金元素Pb的宏观偏析得到抑制,并且电流为30Hz、100A的组织优于30Hz、80A的组织。

半金属摩擦材料与灰铸铁滑动摩擦表面层特性的分析研究

半金属摩擦材料具有摩擦系数稳定、耐磨性好、对环境污染小和对偶件表面损伤小等优点，但其在摩擦热和界面应力等因素作用下，表层会发生弹性变形、塑性变形、元素扩散、组分转移和摩擦化学反应等现象。因此，利用扫描电子显微镜、Ｘ射线能量色散谱和差热－热重分析，对铜纤维增强的半金属摩擦材料与灰铸铁滑动摩擦表面层的特性作了分析研究，考察了表面层特性对摩擦磨损行为的影响。结果表明，在给定的试验条件下，半金属摩擦材料摩擦表面形成了富铁贫铜表面层，其所含有机组分的摩擦热分解深度约为０．３５ｍｍ，含铜量为１５％—２０％（ｗｔ）的材料之磨损性能较好，还能在偶件灰铸铁摩擦表面形成比较均匀连续的铜转移膜，龟裂脱落是偶件磨损的重要机制。研究结果可以作为研制和应用半金属摩擦材料的科学依据。

铸态铅黄铜动态再结晶模型的建立

在Sellars基本模型的基础上,通过对实验数据进行回归,建立了铸态铅黄铜动态再结晶模型;用De-form3D软件模拟的结果与实验所测的数据相吻合。采用Gleeble-1500热模拟试验机进行压缩试验,试验条件为应变速率0.0002/s～0.005/s,变形温度540℃～660℃,应变0.1～1.2,初始晶粒尺寸38μm。

铸态铅黄铜准超塑性变形及其机理的研究

通过恒速度拉伸试验，研究了铸态铅黄铜的准超塑性变形行为及其机理。结果表明：在620～680℃，初始应变速率1×10^-4～1×10^-1s^-1范围内材料表现出良好的超塑性。最佳条件为660℃，保温25min后，以初始应变速率1×10^-2s^-1拉伸，SEM断口扫描和TEN透射照片显示：试样为典型的韧窝断裂；变形初期产生大量位错，随着变形逐渐形成亚晶界，进而演变为小角度和大角度晶界，整个过程是由位错的产生及再结晶来实现的。

铸态铅黄铜准超塑性拉伸组织变化的研究

采用单向拉伸对铸态铅黄铜进行了准超塑性研究。在温度相同条件下,在较高的拉伸速度下获得了大伸长率。在相同的速度下,随着温度的升高,动态再结晶现象比较明显。金相组织分析表明,在动态再结晶开始时,新的晶粒首先出现在晶界附近。随着变形量的增加,再结晶区由晶界逐渐向晶粒内部扩展,最后动态再结晶完成,整个晶粒内部完全细化。

两种生产工艺对H65黄铜管组织与性能的影响

对挤压法和"连铸-冷轧"法两种工艺生产的H65黄铜管的组织与性能进行了综合对比研究。结果表明:两种工艺下H65黄铜管成品平均晶粒尺寸相差较小,挤压法工艺约14μm,"连铸-冷轧"法工艺约18μm;"连铸-冷轧"法成品管抗拉强度为335MPa,伸长率为61%,硬度为84.7HV1.0,挤压法成品管分别为360MPa,67.5%和82.6HV1.0,均达国标要求;挤压法成品管平均偏心率约12.5%,而"连铸-冷轧"法成品管偏心率仅为6.2%,且综合成材率较挤压法提高了11%。分析表明,高效短流程的"连铸-冷轧"法H65黄铜管加工工艺具有良好的发展前景。

新型铜合金铸造添加剂对HPb59-1组织和性能的影响

研制了一种新型铜合金铸造添加剂。研究了不同的添加剂加入量对HPb59-1铸态组织和性能的影响,及在不同截面尺寸和不同铸造方法条件下的使用效果。结果表明,不加铜合金铸造添加剂时HPb59-1的铸态组织主要由粗大的α和β相组成,加入添加剂后组织变为细小片状或等轴晶,明显改善铅黄铜的组织形态,有效的细化铅黄铜的组织;加入0.02%的添加剂可以提高铅黄铜的力学性能20%以上;添加剂对不同截面尺寸和不同铸造方法得到的铸件组织,均有较好的细化效果。

铸态铅黄铜的准超塑性及应用

通过恒速拉伸试验,对一种生产保持架用铅黄铜的准超塑性进行研究。由正交试验法确定出最佳超塑性条件;考察了变形温度、初始应变速率对其影响,并测定其力学性能。结果表明:此种不经预处理的铸态铅黄铜,在适当条件下具有一定的超塑性。依据试验结果,生产出高速重载轴承的保持器。

铸态铅黄铜准超塑性变形的动态再结晶模型

采用Gleeble-1500D热力模拟试验机对铸造铅黄铜进行了压缩试验,试验条件中应变速率为0.0002～0.005s-1,变形温度为540～660℃,真应变为0.1～1.2,初始晶粒尺寸为38μm。在Sellars基本模型的基础上,通过对试验数据进行回归,建立了铸态铅黄铜动态再结晶模型,并用Deform-3D软件模拟了铜合金轴承保持架准超塑性成形过程中的动态再结晶,模拟结果与试验所测的数据吻合,表明所建立的铸态铅黄铜动态再结晶模型具有实用性。

船用硅黄铜通海阀壳的砂型铸造工艺

针对几种典型的硅黄铜ZCuZn16Si4通海阀壳的结构特征及容易产生的铸造缺陷,进行了较为深入的探讨,并给出了相应的铸造工艺方案。结果表明,防止了冷隔夹层、缩裂疏松及氧化夹杂等缺陷产生,有效地避免了通海阀渗漏情况,制备了质量可靠的铸件。

海洋环境下ZL115-T5铸铝合金/C41500海军黄铜腐蚀行为研究

目的研究海军某型装备壳体结构材料在海洋环境下的腐蚀行为及规律。方法根据折算出的实验室加速腐蚀试验环境谱,开展了ZL115-T5铸铝合金试验件、ZL115-T5铸铝合金/C41500海军黄铜接触试验件、模拟实际涂抹黄油试验件以及模拟维护涂抹缓蚀剂试验件的实验室加速腐蚀试验。结果得到了该型铝合金在不同服役年限及服役状态下的腐蚀形貌、质量、平均腐蚀深度以及腐蚀损伤度变化规律。结论该型合金在不同服役状态下的腐蚀行为呈现差异化,ZL115-T5铸铝合金与C41500海军黄铜偶合接触会加速铸铝合金的腐蚀,黄油能够在一定程度上抑制电偶腐蚀,但效果并不明显。缓蚀剂能够延缓海洋环境下ZL115-T5铸铝合金腐蚀,其中THFS-10软膜缓蚀剂以及THFS-15长效硬膜缓蚀剂效果较好。

硅黄铜铸件的渗漏缺陷分析

为了满足耐海水腐蚀、高导热率和承压能力要求,冷却器盖均采用硅黄铜制造。某厂在冷却器盖的生产过程中,铸件废品率高达60%,主要问题是铸件在水压测试中出现渗漏。分析了冷却器盖铸件的渗漏缺陷。结果表明:硅的加入量和浇注温度偏高,硅熔化不完全是导致此类铸件产生渗漏的主要原因。针对性地采取措施后,冷却器盖铸件的成品率大幅提高,达到了90%以上。