Experimental study of the Portevin-Le Chatelier effect under complex loading of Al-Mg alloy: procedure issues

The aim of this work is to solve the methodological issues of the experimental study of the nucleation and propagation of deformation bands due to the Portevin-Le Chatelier effect under conditions of complex loading. It is of interest to determine the boundaries of unstable plastic deformation of the AMg6 alloy under complex loading conditions. A technique for controlling the loading process with a given rate of deformation intensity of materials has been worked out. The results showed that short-term stops and unloading during loading influence on the value of critical deformation, at which the manifestation of the jerky flow begins. The evolution of inhomogeneous strain fields and local strain rates under conditions of manifestation of jerky flow during tension with torsion tests of Al-Mg alloy samples.

The Portevin-Le Chatelier effect in corrosion behavior of the Mg-Zn-Sr alloy

The as-solutionized Mg-4Zn alloys, one candidate material for biological implantation, are featured with the Portevin-Le Chatelier effect during the tensile testing with strain rate of 6.67×10-7 s-1, which leads to the higher corrosion rate and the acceleration of stress corrosion cracking. With the increase of the strain, new slip bands are generated and the proliferation of dislocations is very rapid in slip bands. The microgalvanic corrosion occurs between the slip bands (anode) and the low-dislocation-density region (cathode). The 0.1 wt. % Sr addition can reduce the impact of the Portevin-Le Chatelier effect on as-solutionized Mg-4Zn alloy, resulting from the inhibition of twin, the better grain coordination deformation ability and the lower density of geometrically necessary dislocations.

The Domain of Portevin-Le Chatelier Effect in Al-3Mg Alloy

An Al-3Mg (wt. %) alloy was studied after equal channel angular pressing and subsequent cold rolling. The mechanical behavior of the alloy in the temperature range from 223 K to 373 K (from –50°C to 125°C) at strain rates 2.1×10–1 – 5.2×10–5 s–1 was investigated. The analysis of stress-strain curves was performed to determine the conditions of manifestation of the Portevin – Le Chatelier (PLC) effect in investigated alloy. The deformation curve at a temperature of 298 K (25°C) and a strain rate of 1×10–3 s–1 is characterized by instability of plastic flow in contrast to the deformation curves obtained under other studied strain rate/temperature conditions. Stress oscillations at the necking stage were observed at high temperatures (>323 K (50°C)) and lower strain rates (1×10–4 s–1 and 5.2×10–5 s–1) forming the left border of the PLC effect domain. In general, deformation curves are characterized by the absence of stress serrations during the uniform elongation.