Hot tensile test have been performed on Al-Zn-Mg alloy at 250-400°C and 10-3-10-5 s-1 . At the lowest test temperature the stress-strain curves shows a gradual softening after peak while at the other temperatures a plateau is obtained. The microstructural analysis of the polished longitudinal surface of all deformed samples shows that the alloy exhibits cavitation. The cavities have been detected mainly at grain boundaries and particles inclusions. The phenomena limits the hot workability of materials and can cause premature fracture. This paper studies both the relationship between flow curve behaviour and microstructural evolutions and between cavitation, microstructure and process parameters. The main conclusions are the following: 1) Precipitated Zn-Mg particles not are active in crack nucleation, in fact at 250°C cavitation remains almost constant as strain rate decreases. The role of nucleation point of the cavity seems to be related to the constituent particles and segregation as shown by strong reduction of cavitation in the sample solutionized at 490°C-2h before tensile deformation at 250 and 400°C 2) In the investigated range of experimental conditions, the cavity growth is mainly driven by plastic straining and the fracture type is transgranular ductile
Hot tensile behaviour and cavitation analysis in as-cast and solutionized Al-5.5Mg-Zn alloys
LEO, PAOLA;
2012-01-01
Abstract
Hot tensile test have been performed on Al-Zn-Mg alloy at 250-400°C and 10-3-10-5 s-1 . At the lowest test temperature the stress-strain curves shows a gradual softening after peak while at the other temperatures a plateau is obtained. The microstructural analysis of the polished longitudinal surface of all deformed samples shows that the alloy exhibits cavitation. The cavities have been detected mainly at grain boundaries and particles inclusions. The phenomena limits the hot workability of materials and can cause premature fracture. This paper studies both the relationship between flow curve behaviour and microstructural evolutions and between cavitation, microstructure and process parameters. The main conclusions are the following: 1) Precipitated Zn-Mg particles not are active in crack nucleation, in fact at 250°C cavitation remains almost constant as strain rate decreases. The role of nucleation point of the cavity seems to be related to the constituent particles and segregation as shown by strong reduction of cavitation in the sample solutionized at 490°C-2h before tensile deformation at 250 and 400°C 2) In the investigated range of experimental conditions, the cavity growth is mainly driven by plastic straining and the fracture type is transgranular ductileI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
