氟铝酸铯—氟铝酸钾铝钎剂的合成

【作者】 贺军四；

【导师】 杨占红； 陈志祥； 蔡志红；

【作者基本信息】 中南大学 ， 应用化学， 2009， 硕士

【摘要】 在铝及铝合金的钎焊过程中,应用较广泛的无腐蚀硬钎剂是Nocolok（KF-AlF₃）钎剂。该钎剂熔化温度558℃,最大不足在于操作温度（600℃）过高,一多半的铝合金由于过烧温度低于600℃而不能用该钎剂。因此,要求无腐蚀、水不溶而熔化温度又较低的钎剂,成为十余年来钎剂发展的重要方面。一个有可靠应用前景的钎剂是CsF-AlF₃系。从CsF-AlF₃系的相图可以看出,可用作钎剂的共晶点E₂含x（AlF₃）=42.0mol%,x（CsF）=58.0mol%,熔化温度471℃。但CsF的价格很贵,对钎剂研究的重点在于降低该类钎剂的成本,同时又能保证其活性。因此,研究CsF-AlF₃-KF三元系钎剂,无论是在进一步调整钎剂的熔化温度、改善性能和降低钎剂的成本方面,都有很大的意义。大多数文献都只从理论方面推测该三元钎剂的可行性,虽具有一定的指导意义,但并未在实际应用可行性方面做深入研究。关于以CsF-AlF₃-KF系作为钎剂的报道很少,尤其是作为钎剂在铝及铝合金焊接过程中的钎焊未见报道。本文以CsF-AlF₃-KF三元相图为基础,以碳酸铯、碳酸钾、氢氧化铝和氢氟酸为原料,用化学合成法配置了一系列不同摩尔比例的试样,对该试样进行熔清和摊流试验,从中选择能熔清、摊流面积较大、CsF含量较少的FM-2试样（AlF₃:CsF:KF=43mol%:18mol%:39mol%）,对其进行改进。采用耐驰STA409PC型差示扫描量热分析仪测定了钎剂的熔点;D/MAX2200VPC粉末X射线衍射仪分析其物相组成;S-3400N扫描电子显微镜分析颗粒形状;按照GB11364-89《钎料铺展性及填缝性试验方法》测定钎剂的铺展面积;搭配Zn-Al30的钎料,采用搭接方法,高频钎焊工业纯铝,CMT4204型微机控制电子万能拉力试验机测试其剪切强度。结果表明:FM-2-4钎剂的熔点为520℃左右,CsF含量较少,成本低,熔点较低;其主相为Cs₂KAl₃F₁₂,次相为K₂AlF₅·H₂O和KAlF₄;钎剂形貌较单一和规则;560℃时FM-2-4和FM-2-5的铺展面积较大,均比540℃大;钎焊接头剪切强度为55MPa,接近母材强度,满足实际钎焊要求。本文还研究了钎缝组织与力学性能的关系,用金相显微镜和MH-5D型显微硬度计观察了钎焊接头的显微组织并测试其硬度;JCM-5700型分析扫描电子显微镜观察断口形貌。结果表明:FM-2-4（AlF₃:CsF:KF=A4:C2:K4）和FM-2-5（AlF₃ :CsF:KF=A5:C2:K5）钎焊接头未见有气孔、夹渣、裂纹等焊接缺陷;硬度以钎焊缝中心处最高,钎焊缝与母材结合处次之,母材硬度最低;FM-2-4和FM-2-5断口为韧性断裂,宏观结果表现为剪切强度较高。抗拉强度、金相组织和钎缝断口形貌之间存在密切的关系。更多还原

【Abstract】 As a non-corrosive brazing flux, the Nocolok flux（KF-AlF₃） is widely used in brazing aluminum and its alloys. The melt point of this flux is 558℃and the biggest disadvantage in brazing is the operation temperature （600℃） is too high for most of the aluminum alloys whose collapsed temperature are lower than this , so they cannot braze with it. Therefore, it has becoming an important aspect for developing a flux which has the features of non-corrosive, insoluble and low melt point.The system CsF-AlF₃ is a reliable application prospect flux. From the phase diagram we can see that, the eutectic point E₂ contains x（AlF₃）42.0 mol% and x（CsF）58.0 mol% and the melt point is 471℃. But the price of CsF is expensive, therefore the emphasis of the research for fluxes is decreasing the cost and improving the activity. So it has great sense to study the ternary system CsF-AlF₃-KF for adjusting the melt points improving the performance and decreasing the cost. Most of the papers are conjecturing the feasibility of the ternary system CsF-AlF₃-KF from the theory, which has guide meaning but did not do research in application. There are little reports about the ternary system CsF-AlF₃-KF as a flux, especial in the brazing aluminum and its alloys.Based on the phase diagram of ternary system CsF-AlF₃-KF, this paper prepared a series of samples from cesium carbonate, potassium carbonate, aluminum hydroxide and hydrofluoric acid by chemical method, the samples were investigated by melting and spread ability test, then improved it from the samples that can melt clearly, has larger spread area and low content of CsF which is FM-2（AlF₃:CsF:KF=43 mol%:18 mol%:39 mol%）. Tested the melt point with naichi STA409PC Differential Scanning Calorimetry ; analyzed the structure and pattern of the fluxes with D/MAX2200VPC power X ray diffraction instrument and S-3400N scanning electronic microscope; tested the spread area according to the GB11364-89 <Test procedures of spread ability and clearance fill ability for filler metals> and shear strength by CMT4204 microcomputer controlled electron universal tension test machine with brazing filler metal Zn-Al30, lap joint, high frequency and industrial pure aluminum. The results showed that: the melt point of the fluxes FM-2-4 （AlF₃:CsF:KF=A4:C2:K4）and FM-2-5（AlF₃:CsF:KF=A5:C2:K5） is about 520℃, the content of CsF is low , so the cost is low too ; the main phase of the fluxes is Cs₂KAl₃F₁₂ and the rest are K₂AlF₅·H₂O or （and） KAlF₄; the pattern is simle and regulur; the spread area is large and larger in 560℃than that in 540℃, the shear strength of the brazing joint is 55 MPa, close to the strength of the base metal, meet the requirement of actual brazing.This paper also studied the relationship between the brazing joint and mechanical properties ,tested the microstructure of the brazing joint with metallographic microscope and the hardness with MH-5D micro hardness instrument; observed the fracture pattern with JCM-5700 SEM. The results show that: there are no gas hole, slag patch or crack in the brazing joint with the fluxes FM-2-4（AlF₃:CsF:KF=A4:C2:K4） and FM-2-5（AlF₃ :CsF:KF=A5:C2:K5）; the center of the joint has the highest hardness, larger than the place the joint bonding with the base metal and the base metal is the lowest.; the fracture pattern is gliding with the fluxes FM-2-4 and FM-2-5 so the shear strength is high . There is intimate relationship between the shear strength, metallographic and fracture pattern of the brazing joint.更多还原