【作者】 姜丽丽；

【导师】 吕世雄；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2015， 硕士

【摘要】 近年来,铝钢构件在空调管的连接中以其耐腐蚀,低温使用性能好等特点受到了广泛的重视。铝合金和不锈钢在固态下的互溶度极低,使得界面很容易生成脆性金属间化合物,因而获得优异接头的关键是对铝/钢接头金属间化合物控制。钎焊实现连接是通过液态钎料铺展润湿母材,其连接温度比母材的熔点低,能够一定程度控制金属间化合物的形成。但铝基钎料难以铺展及润湿不锈钢,因此,本文提出了铝合金和预镀层不锈钢钎焊的方法,浸镀铝合金到不锈钢表面,提高钎料的铺展润湿性能,从而获得优异的铝/钢接头。本文系统的研究了预镀不锈钢与铝合金钎焊。通过高频加热热浸镀方法热浸镀一层纯铝或者Al Si12到不锈钢表面,分析不锈钢基体与不同浸镀材料的镀层之间界面的连接特点,借助热力学方法对分析界面的金属间化合物形成规律。以此为基础,研究焊前热浸镀条件下Steel/Al钎焊工艺,采用高频感应和火焰钎焊两种方法,并通过改变浸镀材料、焊接电流、加热时间等条件以保证质量优异的钎焊接头。分析接头的微观组织、反应层形态及产物,建立工艺—组织—性能之间的关系。结合热力学、动力学理论知识及试验结果对界面化合物生长行为及规律进行分析;利用显微硬度,拉伸试验对不同工艺下接头力学性能进行评定,通过断口对接头的断裂行为进行分析。Noclock钎剂作助镀剂条件下,完成了空气条件下不锈钢热浸镀过程。不锈钢在铝液中的浸镀过程为:“不润湿—初始润湿—润湿延展—完全润湿”几个阶段。选用纯铝为镀材时界面反应层为Fe Al3和Fe2Al5;选用Al Si12为镀材时镀层紧密,界面反应层主要为Fe Al3和Fe2Al8Si。镀层条件下改善了接头的润湿性能,接头成形良好,钎焊接头主要由钢—钎缝—反应层—铝四部分组成,钎缝主要有α-Al及Al-Si共晶组织组成。确定合适的高频感应电流为270A~330A,感应钎焊时间为25s~35s。在保证钎料良好润湿铺展条件下,加热时间不变时,随感应电流增加,反应层增厚富铝相增加,钎焊接头力学性能降低;电流不变时,随着加热时间的增加,反应层种类不变,反应层厚度增加,力学性能下降。未浸镀的接头界面是由5~7μm厚的反应层Fe(Al,Si)3和1~2μm的锯齿状的反应层Fe2Al8Si组成;选用纯铝作镀层的反应层主要由3~5μm边缘呈凸起状的Fe(Al,Si)3和1~2μm平直反应层Fe(Al,Si)2组成;选用Al Si12作浸镀材料的界面反应层可以分为三层。镀层条件下,钎料的润湿性提高,润湿铺展时间减少,热浸镀过程形成的反应层能够有效的阻碍钎焊时界面元素的扩散,使反应层厚度减薄及界面反应成分改变。采用热浸镀纯铝的钎焊接头的力学性能较焊前未热浸镀102Mpa提高到1642.Mpa,提高了近60%,并且断裂在母材侧。更多还原

【Abstract】 In recent years, the hybrid structures of aluminum and stainless steel, which are widely valued in the field of air conditioning pipe, attract the great attention for its properties of excellent corrosion resistance and low temperature performance. Large amounts of brittle intermetallic compounds(IMCS)were formed during welding of aluminum/steel dissimilar alloys due to the great difference in their thermal physical properties. Therefore, the key to obtain excellent joint of aluminum/steel is controlling IMCS. Liquid solder is used to wet parent metal in brazing. Because the soldering temperature is lower than the parent metal melting point, this method can control the formation of IMCS effectively. However, the major problem is the poor wettability of filler metal on steel substrates, retards its research and application on joining of aluminum/steel hybrid structures. Thus brazing of precocating-steel and present to get good quality joints.Aluminum coating on stainless steel was applied to enhance the wetability and spreadability of the filler and control the growth of IMCS.This paper has developed systemic research on joining of Al/Steel dissimilar alloys with brazing method. Firstly,a layer of aluminum or Al Si12 was plated on the surface of stainless steel by hot-dipping. Interface Structures of the stainless and dip coating with different coating materials have been researched and analyzed. The wetting process of liquid Al on solid steel during hot-dip aluminize has been analyzed. The interfacial characteristic and the interface compounds forming rules has been analyzed through thermodynamic calculation. Based on the conditions, research of precoating stainless steel/Al brazing techniques, using high frequency induction brazing and flame brazing two methods to obtain a good brazed joints by changing the dipped material, welding current, the heating time and other conditions. Then, we compare and analyze the microstructure, interfacial reaction layer morphology and phase characteristics of the joints with different brazing parameters. We build the relationship of technology, organization and performance. Finally, we combin with the thermodynamics, kinetics theoretical knowledge and test results to analysis growth behavior of the interface reaction layer; Mechanical properties of brazed have been evaluated and analyzed by micro-hardness, tensile test.The results showed that uniform aluminized coating was obtained through hot-dip aluminum method with the assistance of flux under atmospheric conditions. Stainless steel is immersed in liquid aluminum plating process has four stages including: non-wetting, incipient wetness, wetting extension and complete wetting. The interfacial layer was composed of Fe2Al5 and Fe Al3. Hot-dip Al Si12 tight reaction layer was composed of Fe Al3 and Fe2Al8 Si. In brazing procedure, coating improves the solder wettability on stainless steel. Brazed joint is mainly composed of steel, brazing seam, reaction layer and aluminum. brazing seam is mainly composed of α-Al and Al-Si eutectic. It has been identified that the proper frequency brazing current is 270 A ~ 330 A, brazing time is 25 s ~ 35 s. To maintain a good solder flux conditions, the heating time is constant, with the induced current increases, the reaction layer thickness and aluminum-rich phase increase, the mechanical properties decrease; When the current is constant, with the increase of heating time, kinds of reaction layer are same, the reaction layer thickness increases, the mechanical properties decrease.Not-dipped interface reaction layer is mainly composed of 5~7μ m Fe(Al,Si)3 and 1~2μ m serrated Fe2Al8Si; Hot-dipped aluminum reaction layer is mainly composed of 3~5μ m edge shaped Fe(Al,Si)3 and 1~2μ m flat Fe(Al,Si)2; When hot-dipped Al Si12, interfacial reaction layer can be divided into three layers distinctly. With the inhibition of hot dip reaction layer, growth of the interfacial layer was suppressed. As a result, thickness of the interfacial layer decrease. The shear strength of hot-dipped aluminum brazed joint is 164.2MPa which is higher than not hot-dipped aluminum brazed joint whose shear strength is 102 MPa and the fracture location is in base metal.更多还原