Aluminum based alloys equally exhibit low density and good mechanical properties. Reinforcement of such alloys with Mg2Si can lead to additional improvements in the mechanical properties, especially in thermal resistance, together with a reduction in density. Only a low Mg2Si- content can be reached in aluminium alloys using a common process. A fine distribution and high Mg2Si-content (> 15 mass-% Mg2Si) can be achieved by spray forming.Due to its higher solidification rate the formation of undesired phase morphologies is suppressed by this production technique. Aluminum alloys with Mg2Si-contents of 22-34 mass-% were successfully spray formed and were subsequently extruded and heat treated. Additional alloying with 1.8 mass-% copper leads to a further increase in strength by metastable Al-Cu-phases. The microstructure, density and mechanical properties of these new light-weight aluminum alloys have been investigated. The size of the primary Mg2Si-particles in the alloys was not influenced by extrusion or heat treatment while changes in the other phases were observed. An increase in Mg2Si-content reduces the density to below 2.5 g/cm(3) while improving the mechanical properties. During tensile tests at elevated temperatures the material exhibits good thermomechanical resistance. The Mg2Si particle size, obtained by variations in the spray forming prozess, had a significant influence on the mechanical properties. Applications for the new light-weight aluminum alloys can be expected wherever a reduced density together with high hot yield strength would lead to a more compact design in high temperature environments, such as in combustion engines.

Abstract The process chain, typical for additive laser beam powder bed fusion manufacturing of TiAl6V4 components in the aerospace industry, includes hot isostatic pressing (HIP) to reduce the initial porosity. The comparably high temperatures and pressures required by this process, are likely to affect the microstructure and thus also the material properties. Specific variations of the HIP parameters are examined by means of controlled HIP cycles. The parameter variations were kept within conventional boundaries of aeronautics specifications. Specific tests designed to more clearly point out any interdependencies and potential benefits to HIP were also conducted using parameters deviating from the conventional ones. The influence of the HIP parameters was examined using hardness measurements, tensile tests and optical microscopy. Some samples were also examined under a scanning electron microscope. The examinations show that, especially as HIP temperatures rise, the α-lamellae in typical microstructures created by this manufacturing process will grow, reducing strength and simultaneously increasing ductility. It could also be shown that average cooling rates of 75–3000 K/h did not measurably change the microstructure or static properties. As opposed to this, specific quenching at rates of 18 000 K/h during hot isostatic pressing and subsequent ageing for 20 h at 500 °C will create secondary structures comprising α-needles of < 100 nm width. The resultant local microstructure is significantly finer and will increase strength without decreasing ductility.

The combination of different metallic materials enables the design of lightweight structures with tailor-made properties at global as well as local scale and offers great potential for advanced solutions especially for the aircraft and automobile sector. However, after conventional fusion joining, e. g. after laser beam welding, heat affected zones, porosity or grain growth may occur and impair the local properties. In contrast, by solid-state joining techniques like co-extrusion these disadvantages can be avoided. Therefore co-extrusion exhibits an attractive solution for long products combining aluminium and titanium based alloys. Current investigations have been focused on the co-extrusion of aluminium and titanium, where titanium is the reinforcing element that is inserted in aluminium profiles. In the context of a current research project the formation of the intermetallic layer and the mechanical properties were investigated in detail. In addition to that the influence on the intermetallic layer and the mechanical properties on heat treatment were investigated. The mechanical properties were determined by tensile tests. The intermetallic layers were analysed with light optical microscope, scanning electron microscope and electron probe micro analysis. During the co-extruding an intermetallic layer with a thickness of 1 mu m to 3 mu m arises in the bonding zone between aluminium and titanium partner. Alloying elements from the aluminium alloy enrich in this layer. A subsequent heat treatment leads to an age hardening of the aluminium, however, it does not affect the layer thickness. The tensile tests specimen show different failure locations. The heat treatment leads to increased tensile strength values, but also to a decreased yield strength level.

Abstract The combination of different metallic materials enables the design of lightweight structures with tailor-made properties. In contrast to conventional joining methods, for example fusion welding, by co-extrusion no degradation occurs in the materials structure in the form of heat affected zones or pore formation. Therefore, co-extrusion exhibits an attractive alternative for joining aluminium and titanium based alloys. The performed extrusion experiments were focused on the co-extrusion of aluminium (EN AW-6082) and titanium (TiAl6V4), where titanium is the reinforcing element that is inserted in aluminium profiles. During co-extruding an intermetallic layer with a thickness of 1 to 3 µm arises in the bonding zone between aluminium and titanium. In this layer an enrichment of elements of the aluminium alloy, such as silicon, was observed. The formation of the intermetallic layer and the strength of the compounds were examined at various positions after the co-extrusion and after subsequent heat treatment. The investigation of the intermetallic layer was performed with light optical microscope, scanning electron microscope and electro probe micro analysis. The mechanical properties were determined by tensile tests. The heat treatment led to the intended hardening of the aluminium alloy. However, the layer thickness did not change. The tensile tests specimen showed different failure locations. The heat treatment led to increased tensile strength values, but also to a decreased yield strength level.

The combination of different metallic materials enables the design of lightweight structures with tailor-made properties. In contrast to conventional joining methods, for example fusion welding, by co-extrusion no degradation occurs in the materials structure in the form of heat affected zones or pore formation. Therefore, co-extrusion exhibits an attractive alternative for joining aluminium and titanium based alloys. The performed extrusion experiments were focused on the co-extrusion of aluminium (EN AW-6082) and titanium (TiAl6V4), where titanium is the reinforcing element that is inserted in aluminium profiles. During co-extruding an intermetallic layer with a thickness of 1 to 3 mu m arises in the bonding zone between aluminium and titanium. In this layer an enrichment of elements of the aluminium alloy, such as silicon, was observed. The formation of the intermetallic layer and the strength of the compounds were examined at various positions after the co-extrusion and after subsequent heat treatment. The investigation of the intermetallic layer was performed with light optical microscope, scanning electron microscope and electro probe micro analysis. The mechanical properties were determined by tensile tests. The heat treatment led to the intended hardening of the aluminium alloy. However, the layer thickness did not change. The tensile tests specimen showed different failure locations. The heat treatment led to increased tensile strength values, but also to a decreased yield strength level.

Due to high cooling rates spray forming is an appropriate process to produce aluminum alloys with a high content of Mg2Si. Compared to common casting processes, a fine microstructure can be achieved yielding in improved mechanical properties. In this work, billets were spray formed from the two alloys AlMg15Si8Cu2 (22 mass-% Mg2Si) and AlMg20.5Si11Cu2 (30 mass-% Mg2Si) under different spraying conditions. The analysis of the microstructure showed that the size of Mg2Si dispersoids is very sensitive to process parameters. Besides the well known thermal effects of melt superheat (carried out from -40 K to +170 K) and GMR (varied from 2.0 to 6.3) a strong influence of the scanning frequency of the atomizer nozzle (7 Hz and 15 Hz) could be observed. Similar effects could be found for the occurrence of porosity. A new parameter, the enthalpy flow to gas flow ratio (EGR), was defined from these two parameters of which correlations of Mg2Si dispersoid size and amount of porosity were found.

Spray forming offers the possibility of producing alloys with very fine, homogeneous microstructures. Even materials with high contents of intermetallic precipitates, which cannot be produced by casting because of the high solidification rates required, can be distributed homogeneously. Alloying aluminium with high contents of Mg and Si (>20 wt-%Mg2Si) gives an increase in stiffness plus a significant reduction in density, but a very fine distribution of the Mg2Si particles in the aluminium matrix is required. Therefore, such alloys are commonly produced by spray forming. Post-spraying processes such as forming and heat treatment are generally carried out to optimise properties. To examine the microstructure and hardness as a result of subsequent processing, aluminium alloys with high Mg2Si content (22–30 wt-%) have been produced under a variety of spray forming conditions. The duration and temperature of heating before extrusion were varied. In addition, some specimens were preheated without extrusion. The influence of subsequent heat treatment was investigated by varying the age hardening parameters. Hardness measurements were conducted and the distribution and size of the precipitates were evaluated by light microscopy. Image analysis was used to study the coarsening behaviour of primary Mg2Si. The results indicate that the subsequent processing conditions have a strong influence on the microstructure and hardness of the material. Further, a significant dependence of coarsening rate during subsequent processing on the initial state of the material after spray forming was observed. Knowledge of correlations between process parameters and microstructural development offers the possibility of optimising the hot extrusion and heat treatment parameters for high Mg2Si containing aluminium alloys.

Durch die Kombination von unterschiedlichen metallischen Werkstoffen lassen sich maßgeschneiderte Konstruktionen mit optimierten Eigenschaften herstellen. Die Herstellung von Werkstoffverbunden ist jedoch häufig mit hohen Anforderungen an die Fertigungstechnik verbunden. Schwerpunkt dieser Untersuchung ist das Verbundstrangpressen von Aluminium und Titan. Neben den mechanischen Eigenschaften des Verbundes wurden die Ausbildung der Bindungszone sowie die beim Haftungsaufbau wirksamen Bindungsmechanismen untersucht. Hierbei war neben dem Einfluss der Probenvorbereitung vor allem die Wirksamkeit von unterschiedlichen Haftvermittlerschichten von Interesse. Während Schichten aus Kupfer oder Nickel den Haftungsaufbau aufgrund von Oxidschichtbildung verhindern, können durch Umformung eingegossener Titankerne Festigkeiten von über 100 MPa erreicht werden. Im Vergleich zu alternativen Fügeverfahren tritt eine Beeinträchtigung des Werkstoffgefüges in Form von Wärmeeinflusszonen, Porenbildung oder Grobkornbildung hier nicht auf.

Kurzfassung Legierungen auf Aluminiumbasis zeichnen sich durch eine geringe Dichte bei gleichzeitig guten mechanischen Eigenschaften aus. Die Verstärkung von Aluminiumlegierungen durch Mg2Si kann zu einer weiteren Verbesserung der Eigenschaften, insbesondere der Warmfestigkeit, bei gleichzeitiger Dichtereduzierung beitragen. Durch gängige Gießprozesse lassen sich lediglich geringe Mengen Mg2Si in die Aluminiummatrix einbringen. Das Verfahren des Sprühkompaktierens bietet die Möglichkeit, eine feine Verteilung der Mg2Si-Partikel im Gefüge auch für große Mengen (> 15 Ma.-% Mg2Si) zu erzielen. Eine Vergröberung der Partikel wird hierbei durch hohe Abkühlraten unterdrückt. Aluminiumlegierungen mit Mg2Si-Gehalten von 22-34 Ma.-% konnten mittels Sprühkompaktieren erfolgreich hergestellt werden. Sie wurden anschließend stranggepresst und wärmebehandelt. Allen Legierungen wurde ca. 1,8 Ma.-% Kupfer beigegeben, um eine zusätzliche Steigerung der Festigkeit durch metastabile Al-Cu-Ausscheidungen zu erreichen. Die Werkstoffe wurden zur Beurteilung der Ausscheidungsverteilung metallografisch untersucht. Es konnte gezeigt werden, dass für die untersuchten Legierungen die Mg2Si-Partikelgröße sowohl während des Umformens als auch während der Wärmebehandlung nahezu unbeeinflusst bleibt. Die Form und Verteilung der weiteren Phasen hingegen hängt wesentlich vom Wärmebehandlungszustand ab. Mittels Dichte- und Härtemessungen konnte die Gewichtsreduzierung bei gleichzeitiger Verbesserung der mechanischen Eigenschaften nachgewiesen werden. Die Warmfestigkeit der Werkstoffe wurde anhand von Zugversuchen bei erhöhter Temperatur bestimmt. Ein signifikanter Einfluss der durch Variation der Prozessführung beim Sprühkompaktieren eingestellten Mg2Si-Partikelgröße auf die mechanischen Eigenschaften konnte ausgemacht werden. Anwendungen für diese neuartigen Aluminiumlegierungen sind in Bereichen zu erwarten, in denen geringe Dichten in Verbindung mit hoher Warmfestigkeit gefordert sind, z. B. in Verbrennungsmaschinen. ▪

Aluminium Alloys with a 22 wt.-% Mg2Si content were spray formed. This alloy features a low density and is therefore a superior material for lightweight applications. The main problem in the spray forming of this type of alloy was the occurrence of high porosities. First process optimizations have been performed to decrease porosity under a certain level, so that it can be closed by an extrusion process.

Aluminum alloys with high Mg2Si-content (>10 %) offer the possibility of a significant decrease in density and an increase in stiffness at the same time. But these alloys can hardly be produced in casting processes, due to an oxidation and a generation of pores by hydrogen solubility of the melt. Furthermore, the usual solidification rate is not sufficient for a fine microstructure morphology. A fine distribution of Mg2Si is possible by spray forming, where a coarsening of the particles can be avoided due to a higher solidification rate. Different aluminum alloys with high Mg2Si-content (>10 %) have successfully been produced by spray forming, extrusion and age hardening. Mg-excess as well as Si-excess has been investigated. An additional alloying with copper leads to a further increase in strength by the precipitation sequence of Al2Cu. The new light-weight aluminum alloys have been investigated regarding age hardening, physical and mechanical properties. Densities of 2.5-2.6 g/cm3 and Young´s modulus of approx. 80,000 MPa have been found. Microstructures were dense, homogeneous and of fine morphology. The yield strength of these alloys reached values of approx. 400 MPa after artificial aging, whereby only a slight decrease for the hot yield strength was observed up to a temperature of 200 °C. Applications of the new light-weight aluminum alloys can be expected where a reduced density together with a high hot yield strength would lead to a more compact design in high temperature environments, e.g. in combustion engines.