Influence of Mg and Si Content in Aluminium Alloys on Severe Plastic Deformation Behaviour during Solid-State Coating Deposition using Friction Surfacing

动态再结晶对基于摩擦的固态连接技术的工艺特性和材料流动有重要影响。除了一般的材料特性外，a.o.热容量和高温强度，动态微观结构过程，例如位错运动、晶界迁移、亚结构的形成或相的沉淀，对作用的流动应力具有强烈的影响。这种微观组织机制和摩擦堆焊或类似的固态连接技术过程中的材料行为的相关性至今尚未得到系统的研究。合金元素含量的微小变化，例如铝合金中的合金元素含量的微小变化，需要对工艺参数进行重大调整，迄今为止，这些参数是通过经验或统计方法确定的。在摩擦堆焊（FS）过程中，由涂层材料制成的螺柱围绕其纵向轴线旋转，压在基体上。在短的加热阶段（< 2秒）之后，螺柱材料粘附到基底表面，并且通过剪切软化的螺柱材料来调节旋转相对运动。当附加的平移运动叠加时，塑化的螺柱材料从螺柱上剪切下来并沉积在基底上作为涂层。该工艺所需的热量仅由塑性变形产生。对于铝合金的FS，转速高达4000 1/min，工艺温度达到熔化温度的约80%，冷却速率为30 K/s。虽然应变和应变率只能从剪切层的尺寸估计，显然变形条件是极端的。在如此恶劣的条件下，动态再结晶和流变应力的可用知识非常有限，只有少数关于Gleeble试验和高温高压扭转试验的出版物提供了一些线索。在本项目范围内，FS加工了6种定制铝合金。这些合金中的每一种仅在其Mg或Si含量上不同，从而允许直接比较并由此研究这些合金元素对材料行为的影响。Si含量将提高到17.5wt%，在加工过程中提供不可溶解的硬质相，这将进一步影响变形和再结晶机制。除了检查工艺力和涂层几何形状外，还将对塑性变形的微观结构机制进行XRD，EBSD和TEM研究，并与FS期间的材料行为相关联。FS通常会导致非常低的晶粒尺寸和硬质相的球化。所获得的涂层，这是相关的FS过程中产生涂层通过严重的塑性变形的潜在工业应用的机械性能，将通过本项目范围内的微观力学测试进行评估。

Dynamic recrystallization has a major influence on process characteristics and material flow in friction-based solid state joining techniques. In addition to general material properties, a.o. heat capacity and high temperature strength, dynamic microstructural processes, e.g. dislocation movement, grain boundary migration, formation of substructures or precipitation of phases, have a strong effect on the acting flow stresses. The correlation of such microstructural mechanisms and the material behaviour during Friction Surfacing or similar solid state joining techniques has not been systematically investigated up to today. Small changes in the content of alloying elements, e.g. in Aluminium alloys, require significant adaptations of the process parameters, which are to date established by empirical or statistical approaches.During Friction Surfacing (FS), a stud made from the coating material, rotating around its longitudinal axis, is pressed onto the substrate. After a short heating phase (< 2 s), the stud material adheres to the substrate surface and the rotational relative motion is accommodated by shearing the softened stud material. When an additional translational motion is superimposed, the plastified stud material is sheared off the stud and deposited onto the substrate as a coating layer. The heat required for the process is solely generated from plastic deformation.For FS of Aluminium alloys, rotational speeds up to 4000 1/min are applied, process temperatures reach approximately 80% of the melting temperature and cooling rates range at 30 K/s. Although strain and strain rates can only be estimated from the dimensions of the shear layer, obviously the deformation conditions are extreme. The available knowledge of dynamic recrystallization and flow stresses under such severe conditions is very limited, and only few publications on Gleeble-tests and high-pressure-torsion experiments at high temperatures provide some clues.In the scope of this project 6 custom-made Aluminium alloys are processed by FS. Each of these alloys only differs in its content of Mg or Si, allowing a direct comparison and therewith the investigation of the effects of those alloying elements on the material behaviour. The Si content will be raised up to 17.5 wt%, providing undissolvable hard phases during processing, which will further influence the deformation and recrystallization mechanisms. Besides examining process forces and coating geometry, XRD, EBSD and TEM investigations of the microstructural mechanisms of plastic deformation will be carried out, and correlated with the material behaviour during FS.FS typically results in very low grain sizes and spheroidization of hard phases. The mechanical properties of the obtained coatings, which are relevant for a potential industrial application of the FS process to generate coatings via severe plastic deformation, will be evaluated through micromechanical tests in the scope of this project.