镁—钢无匙孔搅拌摩擦点焊设备与工艺研究

发布时间：2019-07-09 17:21

【摘要】：随着人们对环境保护、资源节约意识的不断深入与提高,结构轻量化已成为现代工业发展的必然趋势。镁及镁合金是目前可应用的最轻的结构材料,钢铁材料则依然是未来汽车材料的中坚力量,为了减轻汽车自重并保证其安全性能,多元材料结构型车体设计越来越受到汽车行业的青睐,而镁和钢的连接件既能减轻整体结构的重量,又能保证结构的强度,因而有着良好的应用前景。但镁合金与钢之间的物理性质差异巨大,使得两者很难实现有效的连接,这已成为国内外共同关注并且急需解决的问题。搅拌摩擦点焊因其接头质量高、经济、高效、清洁节能等优点而具有很高的应用价值与市场潜力,故各个国家的焊接界都对搅拌摩擦点焊技术与新型搅拌摩擦点焊设备进行了大量研究。本文通过对实验室原有无匙孔搅拌摩擦点焊设备及其运行原理的分析,设计制造了“偏心”无匙孔搅拌摩擦点焊设备,与原有设备相比,新设备主要在机身结构、传动方案、焊接方法及控制方式等方面做了改进设计,提高了机身稳定性,减少了噪音和震动,实现了主轴电机和搅拌头之间的“零传动”。通过设计可旋转的工作台,改变了原有的焊接方法,增大了焊点面积,得到了成型美观的圆形焊点;在控制系统方面,采用以PLC与矢量控制变频器为核心的硬件与软件系统设计,使用手动与自动两种控制方式,操作简单,使用方便,提高了焊接效率。使用新设备对3mm厚的AZ31B镁合金和1mm厚DP600镀锌钢进行搭接点焊试验,通过正交试验分析点焊接接头的力学性能,并对接头宏观、微观组织形貌及断口进行分析,研究在新设备与不同的焊接方法下接头的连接机理与断裂方式,结果表明:(1)镁钢无匙孔搅拌摩擦点焊接头质量的影响因素从大到小依次为:轴肩下压量、搅拌头旋转速度、搅拌针伸出量,综合考虑接头力学性能和表面成形效果,得出最优工艺参数为搅拌头转速1200r/min、轴肩下压量0.2mm、搅拌针伸出量1.7mm;(2)与实验室原有设备相比,新设备在相应的参数范围内得到的点焊接头整体力学性能更好,接头最大抗剪切载荷达到10.1KN;(3)接头轴肩作用区结合界面平整,结合界面处生成了宽度为6~9μm不等的“竹节状”中间层,竹节状之间存在裂纹且竹节状的长度各不相同,在一定范围内,随着搅拌头转速与轴肩下压量的增加,中间层的厚度增加;(4)镁钢无匙孔搅拌摩擦点焊接头存在两种断裂方式,轴肩作用区为解理断裂,即脆性断裂;搅拌区为韧脆混合断裂;在原位拉伸过程中发现应力集中最大的部位在点焊接头镁钢两板之间的焊点边缘处;另外,断裂发生在镁与中间层的结合面,即镁钢的拉伸断裂面靠近镁侧,脆性中间层基本上留在了钢侧。
文内图片：

图片说明：Fe-Mg二元相图
[Abstract]:With the development and improvement of environmental protection and resource saving awareness, the light of structure has become an inevitable trend of the development of modern industry. The magnesium and magnesium alloy are the lightest structural materials that can be applied at present, and the steel material is still the medium and strong force of the future automobile materials. In order to reduce the self-weight of the automobile and ensure the safety performance of the automobile, the multi-component material structure type vehicle body design is more and more popular with the automobile industry, The connecting piece of the magnesium and the steel can not only reduce the weight of the whole structure but also ensure the strength of the structure, and therefore has good application prospect. However, the physical property difference between the magnesium alloy and the steel is great, making it difficult to realize the effective connection, which has become a common concern at home and abroad and needs to be solved urgently. The friction spot welding of friction stir welding has high application value and market potential because of its high joint quality, economy, high efficiency, clean energy and so on. In this paper, through the analysis of the original non-key-hole friction spot-welding equipment and its running principle in the laboratory, the "off-center"-free hole-free stirring friction spot-welding equipment is designed and manufactured, and compared with the original equipment, the new equipment is mainly in the body structure and the transmission scheme, The welding method and the control method have the advantages of improving design, improving the stability of the body, reducing noise and vibration, and realizing the "zero drive" between the spindle motor and the stirring head. by designing the rotatable work table, the original welding method is changed, the area of the welding spot is increased, and the round welding point with attractive appearance is obtained; in the aspect of the control system, the hardware and the software system design with the core of the PLC and the vector control frequency converter are adopted, The manual and automatic two control modes are used, the operation is simple, the use is convenient, and the welding efficiency is improved. A new equipment was used to weld the 3mm thick AZ31B magnesium alloy and the 1 mm thick DP600 galvanized steel, and the mechanical properties of the joint were analyzed by the orthogonal test, and the macroscopic and microscopic structure of the joint and the fracture were analyzed. The connection mechanism and fracture mode of the joint between the new equipment and the different welding methods are studied. The results show that: (1) The influence factors of the quality of the welding head of the non-key hole of the magnesium steel are as follows: the pressing amount of the shoulder, the rotating speed of the stirring head, the extension of the stirring needle, the mechanical property and the surface forming effect of the joint are comprehensively considered, the optimal process parameters are obtained, the rotating speed of the stirring head is 1200r/ min, the pressing amount of the shaft shoulder is 0.2 mm, the extension amount of the stirring needle is 1.7 mm, and (2) compared with the original equipment of the laboratory, the whole mechanical property of the spot welding head obtained by the new equipment in the corresponding parameter range is better, the maximum shear load of the joint reaches 10.1 KN; (3) the joint shaft shoulder action area is smooth in combination with the interface, and a "bamboo-section" intermediate layer with the width of 6 to 9 & mu; m is generated at the bonding interface; and the thickness of the middle layer is increased with the increase of the rotating speed of the stirring head and the pressing amount of the shoulder and the shoulder, the thickness of the intermediate layer is increased in a certain range, that is, the brittle fracture is broken; the stirring region is a phloem-brittle mixed fracture; the point where the maximum stress concentration is found in the in-situ stretching process is at the edge of the welding spot between the point welding head magnesium steel and the magnesium steel plate; in addition, the fracture occurs between the bonding surface of the magnesium and the middle layer, that is, the tensile fracture surface of the magnesium steel is close to the magnesium side, The brittle intermediate layer is substantially left on the steel side.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG453.9

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