Investigation and enhancement on bonding by cold bulk metal forming processes

如今，像能源效率和轻量化结构这样的关键词在文献中无处不在。在实现这些目标的过程中，通常采用轻质建筑材料，如铝。然而，高机械要求往往超过材料强度。因此，具有不同物理特性的不同材料（例如铝和钢）的组合已经显示出有希望的结果。冷压焊接已被证明是一种合适的焊接工艺。为了获得良好的粘结，需要高表面放大和接触法向应力。为了增加结合强度，我们发现在第一个资助期，将加入伙伴的初始强度进行匹配是有用的。此外，表面处理对键的形成和强度有至关重要的影响。用车削预成形器进行表面处理的结果是不利的。这与形成过程中山谷中原生表面层的胀形有关，也是这些地区表面扩大受到阻碍的原因。此外，进一步研究了机械和化学表面处理工艺对键形成的影响。特别是涂刷和蚀刻导致合适的结果。为了明确和进一步分析键的形成机制，采用透射电镜和电子能量损失谱对连接缝进行了研究。结果表明，在此过程中未产生金属间相，但形成了一层由氧化铝组成的反应层。同时也证明了该反应层并非来源于连接材料的天然氧化层。根据目前的发现，铁和铝之间的键是基于在成形过程中产生的氧化铝。为了便于将当前的结果转移到工业应用中，设计了一种用于横向挤压的工具，以允许产生平面材料化合物。在第三阶段，将采取进一步措施，如调整残余应力分布和调查表面封闭空隙体积，以提高材料之间的结合强度。研究了反应层的形成机理及其对粘结强度的影响。为了将知识转化为广泛的工业应用，以最小方差的过程可重复性为目标。此外，还将研究在该工艺中使用其他金属组合。将设计一个扭转试验台架，以检验实际载荷下的试件。

Nowadays, keywords like energy efficiency and lightweight construction are ubiquitously present in literature. In working towards realizing these goals, lightweight construction materials such as aluminum are usually applied. However, the high mechanical requirements often exceed the material strength. Thus, a combination of different materials with different physical properties (e.g. aluminum and steel) has shown promising results. Cold pressure welding has proven to be a suitable process for joining.To obtain a sound bond high surface enlargement and contact normal stresses are necessary. To increase bond strength a matching of the initial strengths of the joining partners was found to be useful in the first funding period. Furthermore, it can be stated that the surface preparation has a crucial effect on the bond formation and strength. Surface preparation by turning a preform shows unfavorable results. This is related to a bulging of the native surface layers in the valley during the forming process and is the reason why surface enlargement is hindered in these areas. Additionally, further mechanical and chemical surface treatment processes were investigated according to their influence on bond formation. In particular brushing and etching lead to suitable results. To clarify and further analyze the bond formation mechanisms, the joining seam is investigated by transmission electron microscopy and electron energy loss spectroscopy. It is shown that no intermetallic phases are produced during the process, but a reaction layer composed of aluminum oxide is formed. It was also proven that this reaction layer does not originate from the native oxide layer of the joining materials. According to current findings, the bond between iron and aluminum is based on the aluminum oxide generated during the forming process. In order to facilitate a transfer of the current results into an industrial application, a tool for lateral extrusion is designed to allow for the generation of planear material compounds.During the third period further measures like an adjusted residual stress distribution and an investigation of the enclosed void volume of the surface will be taken to increase the bond strength between the materials. Also, the forming mechanism of the reaction layer and its influence on the bond strength will be studied. To transfer the knowledge into a broad industrial application, the reproducibility of the process with minimum variance is targeted. Also, the use of other metal combinations with this process will be investigated. A test bench for torsional testing will be designed to examine the specimens under realistic loads.