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Abstract:
The paper concerns the application of the acoustic emission (AE) method for the determination of the mechanical properties of continuously cast industrial tin bronze CuSn6P, which reveals tendencies to unstable plastic flow connected particularly with the Portevin–Le Chatelier (PLC) effect. The relations between the jerky flow connected with the PLC effect, AE intensity and the evolution of a fracture of the investigated alloy subjected to the tensile and compression tests have been analyzed. It has been found that the intensity of the oscillation of stresses, observed on the curves σ–ε, coincides with the effect of the instability of plastic deformation PLC type and the recorded signals of the intensity of acoustic emissions. It has also been found that the increase of the tensile temperature in the investigated alloy involves changes in the mechanism of cracking from transcrystalline ductile to brittle intercrystalline, characteristic at the temperature of minimum plasticity (DMT).

Keywords:
Copper alloy, Portevin–Le Chatelier phenomenon, Fractography, Acoustic emission, Intercrystalline fracture

Abstract:
The results of the investigation of both mechanical and acoustic emission (AE) behaviors of Mg4Li5Al and Mg4Li4Zn alloys subjected to compression and tensile tests at room temperature are compared with the test results obtained using the same alloys and loading scheme but at elevated temperatures. The main aim of the paper is to investigate, to determine and to explain the relation between plastic flow instabilities and the fracture characteristics. There are discussed the possible influence of the factors related with enhanced internal stresses such as: segregation of precipitates along grain boundaries, interaction of solute atoms with mobile dislocations (Cottrell atmospheres) as well as dislocation pile-ups which may lead to the microcracks formation due to the creation of very high stress concentration at grain boundaries. The results show that the plastic flow discontinuities are related to the Portevin-Le Châtelier phenomenon (PL effect) and they are correlated with the generation of characteristic AE pulse trains. The fractography of broken samples was analyzed on the basis of light (optical), TEM and SEM images.

Keywords:
lightweight alloys, Acoustic Emission, fracture, Portevin-Le Châtelier phenomenon, twinning, dislocations, shear bands

Abstract:
The results of the investigation of both mechanical and acoustic emission (AE) behaviors of Mg4Li5Al alloy subjected to compression and tensile tests at room temperature are compared with the test results obtained using the same alloy and loading scheme but at elevated temperatures. The main aim of the paper is to investigate, to determine and to explain the possible influence of factors related with enhanced internal stresses such as: segregation of precipitates along grain boundaries or solute atoms along dislocations (Cottrell atmospheres) or dislocation pile-ups at grain boundaries which create very high stress concentration leading to fracture. The results show that the plastic instabilities are related to the Portevin–Le Châtelier phenomenon (PL effect) and they are correlated with the generation of AE peaks. The fractography of breaking samples was analyzed on the basis of light (optical), TEM and SEM images.

Abstract:
The work concerns the application of the acoustic emission (AE) method in testing the mechanical properties of continuously cast industrial tin bronze CuSn6P, which reveals tendencies to instable plastic flow connected particularly with the Portevin-Le Chatelier (PLC) effect. The relations between the jerky flow connected with the PLC effect, AE intensity and the evolution of a fracture of the investigated alloy subjected to the tensile test at a strain rate (?? ) of about 1.2·10-3s-1 in the range of temperatures (20÷400?C) has been analyzed. It has been found that the highest intensity of the oscillation of stresses, corresponding to the instability of plastic deformation PLC occurred at 200?C, whereas the maximum of the AE activity is at about 200÷250?C. The brittle intergranular fracture starts in the range of equicohersive temperature (TE) of about 200?C. Plastic deformation of the investigated alloy in the range of the temperature of minimum plasticity, amounting to about 400?C, results in intercrystalline fractures on the entire surface of the stretched samples.