P 1092 – Quality assurance at electromagnetic pulse welded joints (QuaSi MPS)
During this project, studies were carried out to assess the weldability of a high-strength aluminum alloy EN-AW-6016-T6 with dual-phase steel HCT780X using magnetic pulse welding. The process window for manufacturing sound welded joints with this combination of materials was generated on the basis of numerous test series and validated by the destructive test. The influence of welding process parameters on the welding result was documented. The knowledge gained from this could be transferred to application-related welding geometries.
Possible irregularities during joining of mixed connections (aluminum-steel) using MPS technology were analyzed and characterized. The results were summarized in the form of a defect catalog based on DIN EN ISO 6520-2. The position of the irregularities with regard to the joint surface was described schematically and illustrated by an example using the metallographic examination (cross-section).
The suitability of eddy current thermography as a non-destructive test method for assessing the quality of an MPS connection was examined and proven in the project. The methods required for reproducible imperfection introduction were developed, presented and the test specimens subjected to thermographic testing. A distinction could be made between the defect-free and defect-prone MPS connections. The results of the defect detection with the help of active thermography could also be transferred to application-related magnetic-welded welding geometries. The weld seam area of a magnetic pulse welding and its influence on the strength of the welded joint was examined. The correlation of the effective weld surface and the maximum tolerable shear stress was demonstrated. The size of the weld seam area can thus be used to assess the quality of a MPS connection. With the help of active thermography, the weld seam area of an overlap welded MPS connection could be determined with a measurement duration of approx. 0.2 s. In order to increase the reproducibility and minimize the time required for the evaluation, algorithms have been developed that enable automated determination of the weld seam area both on the basis of microscopic images (evaluation after metallographic examination) and on the basis of the thermograms. The functionality of the algorithms was validated based on the results of the destructive test and the accuracy was estimated.
For further optimization of the evaluation methodology of thermographic examinations, the use of a transient thermal FEM analysis was examined. Various FEM models as well as approaches to define realistic boundary conditions were discussed. A high degree of agreement in the qualitative comparison between thermographic examinations and the simulation results showed the enormous potential of this approach.
The MPS technology provides the user a welding process that enables high-quality connection of demanding material combinations such as high-strength aluminum alloys with dual-phase steels. Eddy current thermography can be used for this welding process as a non-destructive test procedure to assess the quality of an MPS connection. In addition to the detection of weld irregularities, it enables the weld seam area to be determined non-destructively.