Project Details
Projekt
Investigation and enhancement on bonding by cold bulk metal forming processes
Subject Area
Primary Shaping and Reshaping Technology, Additive Manufacturing
Term
from 2012 to 2020
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 227710263
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.
DFG Programme
Priority Programmes
Subproject of
SPP 1640:
Joining by Plastic Deformation
