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Darmstadt, Germany

Korber D.,Institute For Werkstoffkunde | Landgrebe R.,Institute For Werkstoffkunde | Adelmann J.,TU Darmstadt | Hoche H.,TU Darmstadt | Oechsner M.,TU Darmstadt
Praktische Metallographie/Practical Metallography | Year: 2012

Tests have been performed on hot-dip galvanized four point bend specimens to investigate how different levels of compressive stresses and tensile loads under simultaneous thermal activation below the melting temperature of the zinc coatings affect liquid metal assisted cracking (LMAC). While the material volumes under tensile stress developed intergranular cracking, areas under compressive stress - even using a tin and lead alloyed zinc melt - did show no signs of damage The flat specimens tested without superimposed loading did only show intergranular edge defects in the order of several grain layers when ageing during several hours in differently alloyed zinc melts. Moreover, in the context of the tests, the dominating effect of the alloying elements lead and tin could be confirmed for the intergranular crack formation Furthermore, the particular importance of the material condition for the occurrence of the damage by LMAC could be shown by means of the progression of the crack formation in the microstructure. © Carl Hanser Verlag, München Pract. Metallogr. Source

Striewe B.,IWT - Foundation Institute of Materials Engineering | Grittner N.,Institute For Werkstoffkunde | Von Hehl A.,IWT - Foundation Institute of Materials Engineering | Hunkel M.,IWT - Foundation Institute of Materials Engineering | And 5 more authors.
Materialwissenschaft und Werkstofftechnik | Year: 2012

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 μm to 3 μm 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. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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