Aluminium alloys with controlled melting ranges for process-integrated foaming during extrusion

泡沫填充挤出型材提供低密度和良好机械性能的出色组合。然而，这些产品的缺点是需要将发泡嵌体插入到挤出型材中然后胶合到挤出型材上，或者必须将可发泡前体插入到型材中并在单独的热处理步骤中发泡。或者，可发泡前体和结构材料可以一起共挤出，然后在随后的热处理步骤中发泡。然而，这些生产工艺需要额外的处理和热处理步骤。拟议研究项目的目标是开发利用挤出过程中产生的工艺热直接对挤出空心型材进行泡沫填充的基础知识。在第一步中，将研究可发泡前体。这些前体将基于低熔点铝硬焊料。它们的熔化范围需要根据结构材料的成型温度进行调整，在这种情况下，结构材料是锻造铝合金EN AW 6082。开发铝硬焊料需要考虑的最重要的一点是发泡阶段的开始，因为这在材料进入成型区或离开模具时同时发生。有前途的合金将根据其在自由发泡试验中确定的发泡行为进行研究。这将包括添加稳定合金元素和发泡剂，适用于挤出加工。设想可发泡前体的加工路线的另外改变，即第二挤出工艺。 首先，进一步提高发泡性能，其次，提高加工过程中的材料使用率。随后的共挤出试验，使用特殊的挤出模头允许改进的工艺条件控制，将允许获得挤出过程中发泡阶段的工艺窗口。最后，一个原型的挤出和泡沫填充管将进行测试，以评估的微观结构和机械性能的无损和破坏性测试方法。

Foam-filled extruded profiles offer an excellent combination of low density and good mechanical properties. However, the downside of these products is that either foamed inlays need to be inserted into and then glued to the extruded profiles, or foamable precursors have to be inserted into the profiles and foamed in a separate heat treatment step. Alternatively, a foamable precursor and a structural material can be co-extruded together and then foamed in a subsequent heat treatment step. However, these production processes require additional handling and heat treatment steps. The objective of the proposed research project is the development of fundamental knowledge for the direct foam-filling of extruded hollow profiles using the process heat generated during extrusion. In the first step, foamable precursors will be studied. These precursors will be based on low melting aluminium hard solders. Their melting range needs to be adjusted to the forming temperature of the structural material, which in this case will be the aluminium wrought alloy EN AW 6082. The most important point to be considered for the development of the aluminium hard solders is the onset of the foaming phase, as this has occur simultaneously while the material enters the forming zone or when it exits the die. Promising alloys will be investigated based on their foaming behaviour determined in free foaming tests. This will include addition of stabilising alloying elements and foaming agents, adapted for processing in extrusion. An additional change of the processing route for the foamable precursor, i.e. a second extrusion process, is envisaged to. Firstly, to further enhance the foaming behaviour and secondly, to improve the material usage during processing. Subsequent co-extrusion trials, using a special extrusion die allowing for an improved control of the process conditions, will allow for obtaining a process window for the foaming phase during extrusion. Finally, a prototype of an extruded and foam-filled tube will be tested to evaluate the microstructural and mechanical properties by both non-destructive and destructive testing methods.