无铅易切削铋黄铜的制备及腐蚀、切削性能研究

【作者】 覃静丽；

【导师】 肖来荣； 易丹青；

【作者基本信息】 中南大学 ， 材料学， 2008， 硕士

【摘要】 以制备一种新型的无铅易切削铋黄铜合金为目的,以替代现有应用广泛的易切削铅黄铜。采用熔铸挤压的方法制备了易切削铋黄铜棒材,利用XRD、金相显微镜、扫描电镜、动电位极化和交流阻抗等方法研究添加Ti、Al、Ce对铋黄铜的微观组织及耐蚀性的影响。并利用电子万能试验机、金属切削机床等仪器测试了材料的力学性能和切削性能,着重研究了合金的腐蚀过程和切削机理,得出如下研究结果:1)Ce对Cu-Zn-Bi合金铸态组织的细化作用明显,Al对合金加工后的组织具有一定的细化作用。添加了Al的铋黄铜的抗拉强度、屈服强度较Cu-Zn-Bi、Cu-Zn-Bi-Ce和Cu-Zn-Bi-Ti高,合金的塑性较好。2)Cu-Zn-Bi合金中铋主要以薄膜状存在合金中,而Al、Ce的添加使得Bi的反润湿效应明显,添加了Ti、Al、Ce后,薄膜状的铋减少,主要以颗粒状存在于合金中。Cu-Zn-Bi和Cu-Zn-Bi-Al的平均脱锌层厚度在300μm左右,而Cu-Zn-Bi-Ce的耐腐蚀性能较差,脱锌层的平均厚度大于1000μm。3)分别研究了Cu-Zn-Bi和Cu-Zn-Bi-Al合金在1.0%CuCl₂溶液中的微观腐蚀形貌,发现挤压态合金的腐蚀表面存在一定的微裂纹,分析了腐蚀表面裂纹形成的微观机制,认为其主要是腐蚀过程和样品中的拉应力共同作用的结果。测量其在1.0%CuCl₂溶液中的开路电位,分别为-40.72mV和-144.67mV。4)研究了Cu-Zn-Bi和Cu-Zn-Bi-Al合金在1.0%CuCl₂溶液中不同浸泡时间的交流阻抗图谱,分析表面膜形成过程,得到腐蚀的等效电路图。由腐蚀过程可知,其表面膜在腐蚀6h前形成,6h后被溶液中的Cl^-侵蚀,表面膜破坏。Cu-Zn-Bi-Al合金中的表面膜先于Cu-Zn-Bi中的表面膜形成,Al的加入有利于合金中保护膜的生成。5)根据脱锌层厚度计算了添加不同合金元素的铋黄铜中锌的扩散系数,其扩散系数的数量级在10^-10～10^-9之间,Cu-Zn-Bi-Al的扩散系数较Cu-Zn-Bi的小,而Cu-Zn-Bi的扩散系数较Cu-Zn-Bi-Ce的小。6)Cu-Zn-Bi-Ti合金中,随着铋含量的增加,合金的切削性能提高;Cu-Zn-Bi-Al的切屑细小,呈针状,三向切削力均小于HPb59-1,切削性能优异;Cu-Zn-Bi-Ce的切屑主要呈螺旋状和小片状,但其切削力较HPb59-1有所增大。7)研究了切削热对变形区的影响,发现切削变形时,在铋颗粒中产生的热应力,在温度变化很小时已经超过了铋颗粒的屈服应力,使铋颗粒发生变形。并应用Griffith的断裂理论计算了断屑时铋颗粒的临界尺寸,计算得到只要铋颗粒的尺寸达到0.3446μm时,切屑发生断裂。8)所制备的Cu-Zn-Bi-Al合金具有较高的强度、塑性,耐腐蚀性能良好,并具备优异的切削性能,达到了预期的性能指标,可以替代现有的广泛应用的铅黄铜,具有一定的应用前景。更多还原

【Abstract】 The purpose of this study is to develop a new kind of easy cutting leadless bismuth brass, which is to substitute for the widely used toxic leaded brass. In this work,the easy cutting bismuth brass was fabricated by melting, casting and extruding processes. The effect of adding Ti, Al and Ce on the microstructure and corrosive properties were studied by X-ray diffraction,optical microscope, scanning electron microscope , potentiodynamic polarization and electrochemical impedance spectroscopy, The mechanical property and machinability were tested by electron universal test machine and metal stock removing machine. The corrosion process and fundamentals of the cutting process were mainly discussed. The following results were obtained:1) By adding Ce to the Cu-Zn-Bi alloy,the as-cast micro-structure of Cu-Zn-Bi-Ce alloy was refined. The grain size of as-extruded and annealed Cu-Zn-Bi-Al alloy were smaller than Cu-Zn-Bi, Cu-Zn-Bi-Ce and Cu-Zn-Bi-Ti alloys at the same condition. The ultimate tensile strength and yield strength of Cu-Zn-Bi-Al were much higher than the other three alloys, and also Cu-Zn-Bi-Al alloy has good plastic property.2) The Bi exist as film along phase bounaries in Cu-Zn-Bi alloy , but the Bi film changed to particles with the addition of Ti, Al and Ce. The average dezincify layer of Cu-Zn-Bi and Cu-Zn-Bi-Al alloys are about 300μm,but the corrosion layer of Cu-Zn-Bi-Ce is more than 1000μm.3) The microstructure of the Cu-Zn-Bi and Cu-Zn-Bi-Al alloys in 1.0%CuCl₂ solution were examined. Also examined the mechanism of crack formation process on the corrosion surface , and it is a result of effects of corrosion and residual stress. The open potential of Cu-Zn-Bi and Cu-Zn-Bi-Al are -40.72mV and -144.67mV.4) The typical Nyquist plots with different immersion time of Cu-Zn-Bi and Cu-Zn-Bi-Al alloys were examined, and the equivalent circuit were obtained. The formation of protection film of the alloys were studied, and it was found the film was formed before immersing 6h, and the film was destroyed by Cl^-. The adding of element Al accelerate the formation of the protection film.5) According to the depth of the corrosion layer, the diffusion coefficient of Zn were calculated , and the order of magnitude of it is 10^-10～10^-9. The diffusion coefficient of Cu-Zn-Bi-Al is much lower than that of Cu-Zn-Bi, but the diffusion coefficient of Cu-Zn-Bi is lower than that of Cu-Zn-Bi-Ce.6) With the increasing of Bi content, the machinability of Cu-Zn-Bi-Ti alloy improved. The chip of Cu-Zn-Bi-Al is needle like, and the cutting force is lower than that of HPb59-1. The chip of Cu-Zn-Bi-Ce is helical, but the cutting force is much higher than HPb59-1.7) The effect of cutting heat on the deformed area was also studied. It was found a slim change of the temperature can lead to the heat stress of Bi, which can result in the deform of Bi. According to the fracture theory of Griffith, the critical dimension of Bi was calculated, which is 0.3446μm.8) Cu-Zn-Bi-Al alloy has good mechanical properties,corrosive nature and machinability. It can substitude for the widely used leaded brass and have a pratical application.更多还原