No abstract

After the extrusion process most aluminium alloy profiles don´t satisfy the necessary strength requirements. An increase of strength can be obtained by age hardening of hardenable aluminium alloys. Age hardening includes the three steps of solution annealing, quenching and aging and is usually carried out in a separate process after extrusion. The integration of the sub-steps solution annealing and quenching in the extrusion process results in a marked reduction of the complete process chain. The applicability of this integration depends primarily on the quenching power of the cooling module and on the quench sensitivity of the aluminium alloy. Using the finite element method the non-steady-state process of quenching the profiles after leaving the extrusion press has been simulated. The boundary conditions for quenching are varied for a gas nozzle field and a spray cooling using heat transfer coefficients based on experiments. The simulation results support the design of gas nozzle fields or spray cooling for the extrusion process of different aluminium alloys.

Clinching is the manufacturing process of joining two or more metal sheets under high plastic deformation by form and force closure without thermal support and auxiliary parts. Clinch connections are applicable to difficult-to-join hybrid material combinations, such as steel and aluminum. Therefore, this technology is interesting for the application of AISI 304 components, as this material is widely used as a highly formable sheet material. A characteristic feature of AISI 304 is its metastability, i.e., the face-centered cubic (fcc) γ-austenite can transform into a significantly stronger body-centered cubic (bcc) α’-martensite under plastic deformation. This work investigates the effect of heat treatment—a process that involves the formation of an oxidation layer on the sheet surface—on the forming process during joining and the resulting mechanical properties of clinch joints made from AISI 304. For this purpose, different joints made from non-heat treated and heat-treated sheets were examined using classical metallography and advanced SEM techniques, accompanied by further investigations, such as hardness and feritscope measurements. The shear tensile strength was determined, and the fracture behavior of the samples was investigated. Clear influences of heat-treatment-induced surface roughness on the joint geometry and strength were observed.

KurzfassungDas Strangpressen ist ein wichtiges Formgebungsverfahren für metallische Werkstoffe. Die aushärtbaren Aluminium-Knetlegierungen EN AW-6082 und EN AW-7020 besitzen im erwärmten Zustand die für das Strangpressen notwendigen Verformungseigenschaften. Die Festigkeit der Legierungen lässt sich durch das Ausscheidungshärten, bestehend aus den Teilschritten Lösungsglühen, Abschrecken und Auslagern, verbessern. Gelingt es, das Lösungsglühen in den Strangpressprozess zu integrieren, lässt sich so das separate Lösungsglühen einsparen und damit die Prozesskette verkürzen. Beide Legierungen erfordern mittlere bis geringe Abkühlraten, welche bei entsprechendem Profilquerschnitt in einem Gasdüsenfeld erzielt werden können. In dieser Arbeit werden experimentelle Untersuchungen vorgestellt, anhand derer die Möglichkeit beurteilt wurde, Pressstränge aus der Presshitze heraus in einem Düsenfeld abzuschrecken.

The very high cycle properties of Inconel 718 in two different heat treatment conditions were investigated at a test temperature of 500 °C. One condition was optimized for fatigue strength and displayed a finer-grained microstructure, while the second batch had a more coarse-grained microstructure. For the high-temperature ultrasonic fatigue testing, a new test concept was developed. The method is based on the principle of a hot-air furnace and thus differs from the conventionally used induction heaters. The concept could be successfully evaluated in the course of the investigations. The materials’ microstructure was analyzed before and after fatigue testing by means of metallographic and electron backscatter diffraction (EBSD)analysis. The results show a significant influence of the heat treatment on the fatigue strength caused by the specific microstructure. Further, a difference in crack propagation behavior due to microstructural influences and non-metallic precipitations was observed.