Influence of heat cycle and degree of dilution in electron beam welding on the properties and the long-time behaviour of aluminium copper dissimilar material joints in current-carrying parts

轻量化结构的巨大潜力，尤其是在电动汽车领域，在于用铝代替铜。此外，还可以采用铝作为导体，铜作为接触材料（牢固连接）。目前的技术水平主要集中在裂纹敏感型金属间相（IPS）的识别上。除IPS外，根据已进行的试验表明，接头的大部分由Al-Cu混合晶体组成，类似于EN-AW-2xxx合金。对这一点的验证允许将2xxx合金的已知电气和机械性能转移到不同材料的接头上。预计混合晶体的形成会导致强度的增加，但同时也会导致电导率的降低。温度、进给电流和时间等外部影响因素通过扩散和电迁移使连接区结构发生变化。此外，异种材料接头的工艺性能会发生暂时的变化（电阻增加，强度降低）。对这种行为的研究结果将有助于得出有关关节预期寿命的结论。研究项目的目的是全面了解材料结合铝/铜异种材料接头的发展、结构和时间变化（通过电气操作）。电子束焊接的异常快速和精确的光束操作允许实现特定的温度-时间序列和稀释度。这样，在焊接过程中，非必需相的组成和形成（例如具有更高的延展性或导电性）将影响IPS。将尝试在相反的参数（强度和电导率）之间设置预期使用寿命的最佳值。

A great potential for light-weight construction, above all in the field of electro-mobility, lies in the substitution of copper by aluminium. It is, moreover, possible to apply aluminium as a conductor and copper as a contact material (firmly bonded joining). The state of the art, so far, has put the focus only on the identification of the crack-sensitive intermetallic phase (IPS). Besides the IPS, the larger part of the joint consists of an Al-Cu mixed crystal which is similar to an EN-AW-2xxx alloy, as suggested by the tests which have been carried out. A verification of this allows the transfer of the known electric and mechanical properties of 2xxx alloys to the dissimilar material joint. It is expected that the mixed crystal formation leads to the increase of strength but, at the sime time, to a reduction of the electric conductivity. External influential factors, such as temperature, currentfeed and time bring about the change of the joining zone structure by diffusion and electro-migration. Moreover, a temporal change of the technological properties (increase of the electric resistance, reduction of strength) of the dissimilar material joint will occur. Findings about this behaviour will allow to draw conclusions about the expected lifetime of the joints.The aim of the research project is to achieve overall comprehension about develoment, structure and temporal changes (by electric operation) of the material-binding aluminium / copper dissimilar material joints. The exceptionally fast and precise beam manipulation of electron beam welding allows to achieve specific temperature-time sequences and dilution degrees. This way, the IPS shall be influenced during the welding process with regard to compositon and formation of unrequired phases (for example with higher ductility or electric conductivity). An attempt will be made to set the optimum for the expected service life between the opposedparameters (strength and electric conductivity).