Optimization of friction stir welding process for joining of aluminum to steel

背景 搅拌摩擦焊(FSW)是一种固态焊接工艺，可以对多种难以焊接的材料进行高质量的焊接。由于所使用的能量输入较低，FSW可创建高强度的接头，同时减少变形。由于能够处理大批量生产所固有的变化，搅拌摩擦焊的优势还包括改进的工艺稳健性和降低的生产成本。搅拌摩擦焊在制造轻质结构方面迅速获得认可。对提高燃油经济性的日益增长的需求推动了交通工具用创新铝产品的开发。然而，汽车上使用的大部分结构都是钢的，在钢结构中使用轻质材料引起了人们的极大兴趣。钢和铝合金的组合在制造中的使用越来越多，人们已经投入了大量的努力来焊接钢和铝合金。 问题陈述 虽然搅拌摩擦焊连接铝和钢的好处是显而易见的，但由于对工具的严格要求，搅拌摩擦焊在高熔点合金上的应用受到了限制。 搅拌摩擦焊工具暴露在严重的应力和高温下，特别是在焊接钢等硬质合金时，这会促进工具退化。对于这些合金，由于搅拌摩擦工具成本高、寿命短，限制了搅拌摩擦工具的商业应用。磨损对钢的搅拌摩擦焊刀具寿命有很大影响。因此，重要的是要识别和了解目前存在的磨损机制。刀具磨损受许多因素的影响，包括刀具和工件材料的组成、焊接操作的性质、焊接条件和机床设置以及刀具几何形状。 方法建议和预期结果 在搅拌摩擦焊中，仅对刀具磨损机理进行了有限的研究。拟议项目的目标是确定用于生产铝-钢搅拌摩擦焊接头的工具的主要磨损模式，并解释导致工具磨损和失效的机制。借助现有的磨损模型，将确定在搅拌摩擦焊中影响刀具磨损行为的关键因素。这些知识将用于优化焊接条件和工具性能。这种不同类型焊接的主要磨损机制的确定将对加拿大工业产生重大影响，因为它可能用于汽车和其他工业部门。对于汽车行业来说，以铝代钢将减轻车辆的重量，从而减少燃油消耗和温室气体排放。

Background Friction stir welding (FSW) is a solid-state welding process, which can produce high quality welds of several materials difficult to weld. Due to the low energy input used, FSW creates high strength joints with reduced distortion. Being capable of handling variations inherent to high volume production, advantages of FSW also include improved process robustness and reduced production costs. FSW has rapidly gained acceptance for the manufacturing of lightweight structures. The rising demands for improved fuel economy have driven the efforts for the development of innovative aluminum products for transportation vehicles. However, the majority of the structures used in vehicle involve steel and the employment of lightweight materials in steel structures is of great interest. The use of the combination of steel and aluminum alloys has been increasing in fabrication and many efforts to weld steel to aluminum alloy have been invested. Problem statement Although the benefits of FSW to join aluminum to steel are clear, the applications of FSW to alloys with high melting temperature have been limited due to stringent demands on the tool. The FSW tool is exposed to severe stress and high temperatures particularly for the welding of hard alloys such as steels, which promotes tool degradation. For these alloys, the commercial application of FSW is limited by the high cost and short life of FSW tools. Wear has a huge influence on tool life of FSW of steel. Therefore, it is important to identify and understand the wear mechanisms present. Tool wear is influenced by many factors, which include the composition of the tool and the workpiece material, the nature of the welding operation, the welding conditions and machine setup and the tool geometry. Methodology proposal and expected results In FSW, only limited work has been done on tool wear mechanisms. The goal of the proposed project is to identify the primary wear modes of tools used to produce aluminum to steel FSW joints and to explain the mechanisms contributing to tool wear and failure. With the help of existing wear models, critical factors that influence the behavior of tool wear in FSW will be identified. This knowledge will be applied to optimize welding conditions and tool performance. The identification of dominant wear mechanisms for this type of dissimilar welding will have a significant impact on the Canadian industry, because of its potential for the automotive and other industrial sectors. For the automotive industry, replacing steel with aluminum will decrease the weight of vehicle resulting in reduced fuel consumption and greenhouse gas emissions.