【作者】 刘甲坤；

【导师】 赵洪运；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2011， 硕士

【摘要】 铝合金/不锈钢异种金属结构能够有效的发挥两种材料的优势,具有比重轻、强度高、耐蚀性优良等特点,在航空航天、交通运输等部门具有越来越广泛的应用。由于铝合金及不锈钢两种材料在热物理性能及力学性能等方面存在着巨大差异,在反应过程中极易生成脆性的金属间化合物,降低接头的力学性能,是焊接领域的难点问题。尽管压力焊、钎焊等方法能够实现两者的连接,但上述方法工艺条件苛刻,一般要求工件具有一定的尺寸形状,相比而言,电弧熔-钎焊方法因具有热输入量小,操作方便且易于实现自动化等特点,在铝/钢连接领域具有特殊的优势。本文针对铝/钢异种金属焊接特点,采用CP焊机对铝合金与不锈钢进行电弧熔-钎连接,分别采用在不锈钢表面进行预镀锌、预涂层及预渗铝处理,来促进电弧作用下液态钎料在钢板表面的润湿铺展,分别对1mm及3mm试样开展了搭接和对接试验研究。在此基础上,对不同工艺条件下的接头外观形貌进行了对比分析,并深入研究了接头不同区域的微观组织,并评定了接头的力学行为,建立了组织结构与力学性能之间的联系。1mm铝合金/不锈钢预镀锌搭接接头研究结果显示,随着焊接热输入的增加,界面区化合物层的厚度由2μm增加到10μm左右,靠近界面层熔化区内有τ6-Al4.5FeSi相生成;当焊接热输入为83.44KJ/m时,接头拉剪强度最大为193.4MPa,界面层压剪强度稳定在105-120MPa之间;采用纯铝焊丝的接头压剪强度最大为124MPa;采用Al-Si12焊丝的接头熔化区硬度最大,但仍低于母材硬度。1mm铝合金/不锈钢预涂层搭接接头研究结果表明,随着焊接热输入的增加,化合物层因自身的脆性而碎化进入熔化区;当焊接热输入为86.9KJ/m时,接头拉剪强度最大可以达到190MPa左右;接头的断裂形式分为从靠近铝侧热影响区的焊缝塑性断裂及从界面处脆性剪切断裂两种方式。3mm铝合金/不锈钢预涂层对接接头研究结果表明,预留一定的对接间隙及选取合适的成型槽,接头有良好的成形,未发现碎化及呈针状生长的脆性化合物;接头从界面区发生断裂,抗拉强度可以达到157.8MPa。1mm铝合金/不锈钢预渗铝搭接接头研究结果显示,液态金属在钢板表面的润湿铺展性差,且化合物层有明显的微裂纹存在;接头从界面区断裂,强度仅为60MPa,力学性能较差。更多还原

【Abstract】 Hybrid structures of Aluminum alloy/stainless steel offer the potential to utilize the advantages of the two materials, which are suggested in aerospace and transportation for their light weight, high tension and high corrosion-resistance. It is also a great challenge to join these two materials together because of great differences in thermo-physical and mechanical properties, the easily formation of brittle intermetallic compounds which can reduce the mechanical performance of the dissimilar materials joints. Reliable joints can be obtained via solid-phase welding, brazing and some other processes. However, these methods need either strict technological requirements or workpieces with certain shapes. On the contrary, the arc welding-brazing method has special advantage in aluminum/steel joining because of its small amount of heat input, simple operating and easy to achieve auto-control.Considering the welding characteristics of the aluminum/steel dissimilar metals, CP welding machine was chosen to join aluminum alloy to stainless steel using the arc welding-brazing method. In order to promote the wetting and spreading of filler metal on steel surface, galvanizing coating, precoating layer and aluminized coating were carried out before welding. Lap joints and butt joints were made by Workpieces of 1mm and 3mm in thickness, respectively. On the basis of different processing conditions, appearances of the joints with different weld parameters were analyzed, and microstructures of the joints in different areas were discussed, and mechanical behavior of the joints was assessed and the effect of interface structure on the mechanical behavior of the joints was also studied.The results of lap joints of 1mm aluminum alloy to galvanized stainless steel showed that thickness of the compound layer in the interface area had grown from 2μm to about 10μm along with the increase of welding heat input; a Al4.5FeSi phase was formatted in the melting zone near the interface layer; tensile strength of the joint can reach 193.4MPa when heat input was 83.44KJ/m, and the shear strength of the interface layer was between 105MPa and 120MPa; shear strength of the joint was 124MPa when pure Al filler wire was used; hardness of the seam was biggest when Al-Si12 was chosen as the filler metal but still below that of the aluminum base metal. The results of lap joints of 1mm aluminum alloy to precoated stainless steel showed the compound in the interface layer turned into the melting zone after broken due to its brittle along with the increase of the welding heat input; tensile strength of the whole joint got 190MPa when the heat input was 86.9KJ/m; the fracture mode can be divided into the plastic fracture in the weld seam near the heat affected zone in the aluminum side and the brittle fracture through the interface layer. The result of butt joints of 3mm aluminum alloy to precoated stainless steel showed that joints had a sound double-side forming owing to the joint gap and grooving, and the weld seam consisted mainly of -Al and Al-Si eutectic, in which broken or needle-like brittle compounds were not detected; joints fracture through the interface layer under tensile test with a strength reaching 157.8MPa. The results of lap joints of 1mm aluminum alloy to aluminized stainless steel showed that the liquid metal had a bad spread in the steel surface, and there were fragile intermetallic formed in the interface layer and also obvious micro-cracks between the compound layer and the steel side; the joint cracked from the interface area with a poor strength which was about 60MPa.更多还原