Friction stir welding of dissimilar sheet materials

在运输行业中，对提高燃料效率的需求不断增长，这促使通过增加利用轻质材料（例如铝和镁合金以及复合材料）来减轻重量。然而，在部件制造过程中，主要的挑战是这些材料的焊接，特别是当遇到不同的组合时。即使是类似的合金连接也不是微不足道的，这是由于电弧焊接过程中的裂纹、凝固孔隙和严重变形。涉及纤维增强聚合物复合材料的接头通常需要紧固件或粘合剂，这比焊接更昂贵和耗时。近年来，摩擦搅拌焊接工艺已经成为一种固态焊接技术，与熔焊相比，它提供了许多优点和新的能力。固态焊接的主要特点是通过将材料保持在熔点以下来避免许多传统问题，如开裂和气孔。摩擦搅拌焊接技术使用在端部处具有销形突起的圆柱形工具，该销形突起沿着待接合的材料以搭接焊接或对接接合构造横穿。该建议检查摩擦搅拌焊接的变化，其中点焊可以使用缩回到圆柱形工具中的销进行。关于这种所谓的“再填充搅拌摩擦点焊”方法，只有少数研究被报道，然而，已经证明，与传统的搅拌摩擦点焊相比，可以实现上级接头强度。该工艺可以应用于不同材料的组合，并且这项工作的主要焦点是将铝连接到纤维增强复合材料板。其目的是确定这些材料的再填充搅拌摩擦点焊过程中控制粘合的因素，并确定工艺参数或提供更高接头强度的可能夹层。采用一种专用的填充式搅拌摩擦焊系统研究薄板点焊接头的形成机理。结合的反应，混合，和机械联锁方面的细节将比较焊接参数。先进的电子显微镜技术将被应用于评估的作用，温度和应力的债券形成。接头的性能将使用搭接剪切试验，以及使用宏观尺度和纳米压痕技术的仪器压痕试验进行研究。这将使整体接头强度与焊接过程中形成的微观特征和相关联。拟议的工作将产生必要的知识，以促进在工业中广泛实施这项技术。由于时间、温度、压力和变形控制着接头强度，因此需要了解每个参数的作用。对界面结合的深入研究将有助于确定哪些参数占主导地位，并对接头强度贡献最大。拟议的工作将允许处理地图开发这种技术，也可能适用于其他固态连接过程，包括传统的搅拌摩擦焊。这些图可在以后被加拿大工业利用，以便通过将加工参数与提供最高强度的所需微观结构相联系来快速开发用于连接困难组合的解决方案。这将有助于运输行业利用先进的固态连接技术，以提高其能力并降低制造成本。

There has been a growing need for improved fuel efficiency in the transportation industries, and this has motivated weight reductions through increased utilization of light-weight materials such as aluminum and magnesium alloys, and composites. However, during component fabrication the main challenge is welding of these materials, particularly when dissimilar combinations are encountered. Even similar alloy joining is not trivial, due to cracking, solidification porosity, and severe distortion during arc welding. Joints involving fiber reinforced polymer composites typically require fasteners or adhesives, which are more costly and time-consuming than welding. In recent years, the process of friction stir welding has emerged as a solid state welding technique which offers many advantages and new capabilities compared to fusion welding. The main feature of solid state welding is that many of the traditional problems like cracking and porosity are avoided by keeping materials below the melting point. The friction stir welding technique uses a cylindrical shaped tool with a pin shaped protrusion at the end, which is traversed along the materials to be joined, either in a lap weld or butt joint configuration. This proposal examines a variation of friction stir welding in which spot welding can be conducted using a pin that retracts into the cylindrical tool. Only a few studies have been reported on this so-called ‘refill friction stir spot welding’ approach, however it has been demonstrated that superior joint strength can be achieved compared to traditional friction stir spot welding. The process may be applied to dissimilar material combinations, and the main focus of this work is joining aluminum to fiber reinforced composite sheets. The objective will be to determine factors which control bonding during refill friction stir spot welding of these materials, and to identify processing parameters or possible interlays that provide higher joint strengths. A specialized refill friction stir welding system will be used to study the mechanisms of joint formation in thin sheet spot welds. The details of bonding in terms of reactions, intermixing, and mechanical interlocking will be compared to the welding parameters. Advanced electron microscopy techniques will be applied to evaluate the role of temperature and stress on bond formation. The properties of the joints will be investigated using overlap shear testing, as well as instrumented indentation testing using both macro-scale and nano-indentation techniques. This will allow overall joint strengths to be correlated with microscopic features and phases which form during welding. The proposed work will generate knowledge that is required in order to promote widespread implementation of this technology in industry. Since time, temperature, pressure and deformation control the joint strength, the role of each parameter needs to be understood. A thorough study of the interfacial bonding will help to identify which parameters dominate and contribute most significantly to joint strengths. The proposed work will allow processing maps to be developed for this technique which may also have applicability to other solid state joining processes, including conventional friction stir welding. These maps can be later utilized by the Canadian industries in order to rapidly develop solutions for joining difficult combinations by connecting processing parameters to the desired microstructures which provide highest strength. This will help transportations industries utilize advanced solid state joining technologies in order to increase their capabilities and reduce fabrication costs.