【作者】 朱宏；

【导师】 薛松柏；

【作者基本信息】 南京航空航天大学 ， 材料加工工程， 2011， 博士

【摘要】 铝及铝合金是有色金属中应用最广泛的结构材料,其中6063铝合金具有良好的成型性能、机械加工性能、焊接性能和抗腐蚀性能而广受关注。目前,国内外雷达发射、接收机箱、信号处理机箱广泛采用6063铝合金材料,随着相控阵等先进体制机载雷达的研制生产,为了实现更高的功率密度和高可靠性,铝合金雷达机箱的结构设计日趋复杂,机箱的焊接需要采用“阶梯钎焊”工艺以实现雷达轻量化、高可靠性的目标。根据以上特点,本文寻找出适用于保护气氛炉中高、中温阶梯钎焊6063铝合金的钎料和改进型钎剂,同时研究了钎焊工艺的优化参数。运用正交试验法,通过改变Si,Cu,Ni,RE元素的配比,研究含量的变化对Al-Si-Cu-Ni-RE钎料的熔点、铺展性以及抗剪强度的影响,并通过扫描电镜及能谱分析了钎料内部显微组织;通过研究发现,钎料的成分及加热温度是影响铺展面积的主要因素;对钎料显微组织分析可知,钎料中黑色的脆性θ（Cu Al2）相和区域偏析的絮状相不利于接头的性能,而具有面心立方固溶体的基体相α（Al）以及球状聚集的Si相,使得钎料的力学性能优良。结果表明,Cu元素对钎料熔点的影响最大,其次为Ni,Si,RE元素,钎料的熔点随着Cu含量的增加而急剧下降。选用CsF-AlF₃钎剂和KF-AlF₃钎剂,研究了两种钎剂在6063铝合金表面不同温度下的去膜效果,分析和探讨了钎剂与6063铝合金表面氧化膜的反应机制。研究发现,CsF-AlF₃钎剂是以反应、溶解的机制去除6063铝合金表面氧化膜的,NH4F在高温下生成的HF是CsF-AlF₃钎剂去膜的关键化合物。此外,H2O的存在或形成促进了HF的生成,从而加速了钎剂的去膜进程。CsF-AlF₃钎剂反应产物中没有发现CsF和AlF₃,只有少量的CsAlF4存在。在570℃下,KF-AlF₃钎剂反应产物中以KAlF4为主,而在610℃条件下,KAlF4已不存在,只有少量的KMgF3生成。研究还表明,在610℃条件下,Mg、Mn元素和KAlF4将逐渐地消耗掉,使得钎剂熔点急剧升高,导致钎剂流动性变差。研究和探讨钎焊参数对6063铝合金的中温钎焊接头硬度强度、显微组织和耐腐蚀等的影响。研究表明:在高温钎剂配合下,升温速率在15℃/min以上时钎料即可获得良好铺展,而配合中温钎剂时,对升温速率的要求高于高温钎剂。分别测试了焊后固溶处理、固溶加时效处理及钎焊状态下三种钎焊接头的显微硬度。结果表明:时效处理后的接头硬度最大,钎缝与母材硬度相差不大;固溶处理接头的钎缝处及扩散区显微硬度明显高于母材;钎焊状态下钎缝硬度也较母材硬度高。测试了不同钎焊温度得到的这三种状态的接头剪切强度。结果表明:钎焊温度为560℃的接头剪切强度最高,钎焊温度越低强度越低。观察并分析了升温速率及保温时间对接头显微组织的影响。结果表明:升温速率较慢时,CuAl2枝晶分散不均匀,保温时间过长则Si晶较粗大,CuAl2枝晶变化不明显。采用正交试验法,通过改变Si、Cu、Ni以及混合稀土RE的配比,研究了含量的变化对Al-Si-Cu-Ni-RE钎料的自腐蚀电位、失重质量、腐蚀速率的影响,并通过扫描电镜观察分析了腐蚀前后钎料的内部显微组织。研究发现,钎料的自腐蚀电位与失重质量相对应,随着腐蚀电位的负值增加,失重质量也不断增大。对各元素对腐蚀速率影响的情况分析结果表明,对钎料腐蚀速率的影响依次为Ni的影响最大,其次为Si、Cu、RE。对钎料腐蚀前后的显微组织观察分析可知,Cl-是诱发钎料点蚀的主要原因。腐蚀后的钎料局部区域出现了点蚀,腐蚀后的钎料有明显的网纹状晶间腐蚀。更多还原

【Abstract】 The aluminum and its alloys are widely used as a kind of structural materials, especially the aluminum alloy 6063 is very popular due to its good properties of formability, mechanism weldability and corrosion resistance. The chassis of radar transmitter, receiver and signal processing are manufactured with 6063 in the world. In order to light the weight and improve the reliability, the stepped brazing process is required to braze the radar chassis because of the complicated structure. In this paper, brazing alloys as well as the matched fluxes, which are suitable for brazing 6063 in high and medium temperature with shielding gas furnace, are studied. In the meantime, parameters of brazing process are optimized.The effect of contents on the melting points, spreading property and shear strength of Al-Si-Cu-Ni-RE is researched by changing the level of Si、Cu、Ni、RE according to orthogonal test method. The microstructure of brazing metal is analyzed with SEM and EDS. The results show that the spreading area is dominated by the composition of filler metal and brazing temperature; The black brittle phaseθ（Cu Al2） and macrosegregation flocculent phase decrease the performance of the joint, while the matrix phaseα（Al） with face-centered cubic solid solution and Si phase with conglobulation feature make the performance of the joint better; Cu is the main factor that influences the melting points of the filler metal, next is Ni, Si and RE. The melting points of filler metal sharply lows as the Cu content increases.CsF-AlF₃ and KF-AlF₃ series fluxes are selected to research the effect of the fluxes on removing the oxide film of aluminum alloy 6063 at varied temperature. The reaction mechanism of flux with surface oxide film of aluminum alloy 6063 was analyzed and discussed. The results show that reaction and solution are the mechanism of CsF-AlF₃ removing surface oxide film from Al-alloy 6063 and the HF generated from NH4F at high temperature is the key compound. Moreover, the presence or formation of H2O accelerates the generation of HF, which accelerates the Striping rate of oxide film accordingly. No CsF and AlF₃ except a little of CsAlF4 was found in the reaction product of CsF-AlF₃ flux. The main product of KF-AlF₃ flux is KAlF4 at 570℃and a small amount of KMgF3 but no KAlF4 at 610℃. The results also indicates that Mg, Mn and KAlF4 will be gradually consumed at 610℃, which lead to sharp increasing of melting point and worse flowing property of the flux..The effect of brazing parameters on the hardness, strength, microstructure, and corrosion resistance of 6063 brazing joint is studied. The results show that with high temperature flux, the brazing metal spreads well above the heating rate of 15℃/min, but with intermediate flux, requires for heating rate will be higher than high temperature flux. Micro hardness of three kinds of brazing joints with different treatment is tested. Results indicate that Micro hardness of brazing joint after aging is the highest, of which hardness of the brazing seam and base metal is almost equal. Hardness of brazing seam and its diffusion area of brazing joint after solution is obviously higher than base metal’s. Hardness of brazing seam after brazing is higher than base metal’s, either. Shear strength of three kinds of brazing joints at different brazing temperature is tested. The results show that shear strength of brazing joint at 560℃is the highest, which decreases with brazing temperature. Effect of heating rate and holding time on microstructure of brazing joint is analyzed. Conclusion indicates that CuAl2 dendrites distribute unevenly at slow heating rate and Si grain becomes coarse but CuAl2 dendrites don’t change significantly after long holding time.Effect of contents of Si, Cu, Ni and RE on the corrosion potential, weight loss and corrosion rate of Al-Si-Cu-Ni-RE is studied by changing the level of Si, Cu, Ni and RE according to orthogonal test method. The microstructure is observed with SEM and EDS before and after corrosion test. The results show that the corrosion potential is corresponding to weight loss, the weight loss increased with the decrease of corrosion potential. Ni is the dominant factor that influences corrosion rate, followed by Si, Cu, RE. Cl- is the main reason of inducing brazing metal to pit. Pitting occurred on local area of brazing metal which has obviously reticulate pattern intercrytalline corrosion.更多还原