【作者】 王健；

【导师】 胡勇； 刘德佳； 余永洪；

【作者基本信息】 华东交通大学 ， 化学工程（专业学位）， 2021， 硕士

【摘要】 铝/钢异种金属复合构件是汽车工业“以铝代钢”的重要轻量化结构。但由于Fe在Al中的溶解度很低,Al/Fe异种金属焊接时极易生成脆性金属间化合物,降低了接头力学性能,限制了铝/钢异种金属焊接接头的广泛应用。由五种及五种以上主元形成的高熵合金,能利用高混合熵效应促使形成固溶体,抑制金属间化合物的生成。据此,本论文拟把高熵效应引入至铝/钢异种金属焊接中,通过高熵化设计的焊缝填充材料,利用激光高熵化填粉焊接增加焊缝混合熵值,进而抑制焊缝金属间化合物的生成。相关研究对提高铝/钢焊接接头的安全可靠性,提升我国汽车工业的轻量化制造水平具有重要意义。首先,采用高熵化设计的Ni Cr Mn Si_0.5Cu Ti_0.5填充粉末对DP780双相钢和5083铝合金进行激光填粉搭接实验,通过对比填粉与不填粉两种工艺,探索激光高熵化填粉焊接对焊缝微观结构的演变规律。研究发现,高熵化填粉使焊缝区Fe元素含量显著降低,焊缝Fe-Al金属间化合物明显减少。焊缝区由不填粉试样的马氏体组织变成了高熵化填粉试样等轴晶形貌,焊缝晶粒细化效果明显。但由于搭接时高熵化粉末无法填充至焊缝底部的搭接界面处,使该区域无法实现高熵化,而存在大量的Fe Al₂和Al₂Cu金属间化合物。然后,采用CoZnCuMn_0.8Si_0.2高熵化填充粉末,通过激光高熵化填粉实现304不锈钢与6061铝合金异种金属的对接连接,并探索焊后热处理对高熵化焊缝及焊接界面微观结构的演变规律。研究发现,焊后280℃退火能显著促进高熵化试样焊接界面的元素扩散,使铝侧焊缝边部的Fe元素含量增加。焊后热处理使铝侧过渡区的宽度显著增加,从未热处理试样的～3.4μm增加至6小时试样的～16.5μm。焊后热处理使过渡区内金属间化合物的尺寸显著增加,发现焊后热处理不是调控高熵化焊缝及焊接界面微观结构的有效方法。最后,在CoZnCuMn_0.8Si_0.2粉末焊接304不锈钢与6061铝合金异种金属时改变激光功率,探索焊接工艺参数对Al/Fe异种金属高熵化微观组织与接头性能的影响规律,揭示实现激光高熵化焊接铝/钢异种金属焊缝组织性能调控的有效措施。研究发现,激光焊接功率对高熵化焊缝的各元素含量有显著影响,当焊接功率从500 W下降至400 W时,焊缝区内Al元素含量显著下降,过渡区宽度下降12%。且过渡区内物相结构从500 W试样的Fe Al₂和Fe Al₃演变成400W试样的Fe Al₂。Al/Fe异种金属高熵化焊缝的显微硬度为486～500 HV_0.1,远高于304不锈钢母材的显微硬度,高熵化焊缝具有较好的耐腐蚀性能,其耐盐与耐酸的腐蚀性都与304不锈钢母材相近。更多还原

【Abstract】 Aluminum/steel dissimilar metal composite components are an important lightweight structure in the automotive industry"substituting aluminum for steel".However,due to the low solubility of Fe in Al,brittle intermetallic compounds are easily generated during aluminum/steel dissimilar metal welding,reducing the mechanical properties of the joint,limiting the widespread use of aluminum/steel dissimilar metal weld joints.The high-entropy alloys formed by five or more principal elements can use the high mixing entropy effect to promote the formation of solid solutions and inhibit the formation of intermetallic compounds.Accordingly,this paper intends to introduce the high-entropy effect to the aluminum/steel dissimilar metal welding,through the high-entropy design of the weld filler material,and the use of laser high-entropy powder filler welding to increase the mixed entropy value of the weld,thereby suppressing the weld generating an intermetallic compound.Relevant research is of great significance for improving the safety and reliability of aluminum/steel welded joints and improving the lightweight manufacturing level of my country’s automobile industry.Firstly,the high-entropy-designed Ni Cr Mn Si_0.5Cu Ti_0.5 filling powders were used to carry out laser powder filling lap experiments on DP780 dual-phase steel and 5083 aluminum alloy.The evolution law of powders welding butt weld microstructure.The study found that the high-entropy powders filling significantly reduce the Fe content in the weld zone,and the Fe-Al intermetallic compound in the weld is significantly reduced.The weld zone changed from the martensite structure of the non-powdered sample to the equiaxed morphology of the high-entropy powdered sample,and the grain refinement effect of the weld was obvious.However,because the high-entropy powders cannot be filled to the lap interface at the bottom of the weld during the lap joint,high entropy cannot be achieved in this area,and there are a large amount of Fe Al₂ and Al₂Cu intermetallic compounds.Then,the CoZnCuMn_0.8Si_0.2 high-entropy filling powders were used to realize the butt connection of 304 stainless steel and 6061 aluminum alloy dissimilar metals through laser high-entropy filling powders,and to explore the effect of post-weld heat treatment on the microstructure of high-entropy welds and welding interfaces The law of evolution.The study found that annealing at 280°C after welding can significantly promote the diffusion of elements at the weld interface of the high-entropy sample,and increase the Fe element content at the edge of the weld on the aluminum side.The post-weld heat treatment significantly increases the width of the transition zone on the aluminum side,from～3.4μm for the unheated sample to～16.5μm for the 6-hour sample.Post-weld heat treatment significantly increases the size of intermetallic compounds in the transition zone.It is found that post-weld heat treatment is not an effective method to control the microstructure of high-entropy welds and welding interfaces.Finally,when CoZnCuMn_0.8Si_0.2 powders welding 304 stainless steel and 6061aluminum alloy dissimilar metals,change the laser power,explore the influence of welding process parameters on the high-entropy microstructure and joint performance of aluminum/steel dissimilar metals,and reveal the realization of laser high-entropy Effective measures to control the microstructure and performance of the welded seams of aluminum/steel dissimilar metals.The study found that the laser welding power has a significant effect on the content of each element in the high-entropy weld.When the welding power is reduced from 500 W to 400 W,the Al content in the weld area decreases significantly,and the width of the transition zone decreases by 12%.And the phase structure in the transition zone evolved from Fe Al₂ and Fe Al₃ of 500 W sample to Fe Al₂ of 400W sample.The microhardness of high-entropy welds of aluminum/steel dissimilar metals is 486～500HV_0.1,which is much higher than the microhardness of 304 stainless steel base metal.The high-entropy welds have good corrosion resistance and salt resistance.The corrosion resistance to acid is similar to that of the 304 stainless steel base material.更多还原