Judit Illy

Dislocation structure and work hardening in polycrystalline ofhc copper rods deformed by torsion and tension

Abstract The dislocation structure during work hardening in copper deformed by torsion and tension is investigated by X-ray line broadening and TEM. In the case of torsion the equivalent tensile flow stress and the rate of work hardening is lower than that obtained in tensile experiments. At the same time the dislocation density at the same equivalent strain is considerably larger in the torsionally deformed material and the TEM microstructure indicates a double-slip deformation mechanism. In the tensile deformed samples asymmetric X-ray line broadening indicates long-range internal stresses with relatively lower dislocation densities. In this mode of deformation multiple slip takes place. The lower equivalent flow stress and the smaller rate of work hardening in the torsionally deformed material is correlated with the restricted number of slip systems and the absence of strong long-range internal stresses, which leads to the relative ease of generating high dislocation densities.

Influence of fibre reinforcement on the aging behaviour of an AlSi12CuMgNi alloy

Abstract The aging behaviour of an AlSi12CuMgNi alloy reinforced with 20 vol.% Saffil and Fiberfrax, respectively, has been investigated by hardness measurements and differential scanning calorimetry. Taking the amount of fibres into account, the Saffil-reinforced alloy shows the same heat effect and hardness increase as the unreinforced alloy. In this composite the aging is accelerated, i.e. the maximum hardness is reached in about half the time of the unreinforced alloy. The Fiberfrax-reinforced alloy shows no aging effects at all. This is caused by the formation of an interface layer around the fibres in which Mg is enriched and therefore the formation of Mg2Si precipitates in the matrix is suppressed.

Precipitation and mechanical properties of supersaturated Al-Zn-Mg alloys processed by severe plastic deformation

Supersaturated Al-4.8Zn-1.2Mg-0.14Zr and Al-5.7Zn-1.9Mg-0.35Cu (wt.%) alloys were processed by Equal-Channel Angular Pressing (ECAP) at 200°C. The crystallite size distribution and the characteristic parameters of the dislocation structure of both Al matrix and precipitates were determined by X-ray diffraction line profile analysis, which has been complemented by transmission electron microscopy (TEM) observations. The results show that severe plastic deformation promotes the precipitation process and consequently has a strong influence on the strength of these alloys.

Precipitation microstructure of ultrafine-grained Al-Zn-Mg alloys processed by severe plastic deformation

Supersaturated Al-4.8Zn-1.2Mg-0.14Zr and Al-5.7Zn-1.9Mg-0.35Cu (wt.%) alloys were processed by Equal-Channel Angular Pressing (ECAP) at 200°C. The crystallite size distribution and the characteristic parameters of the dislocation structure of both Al matrix and precipitates were determined by X-ray diffraction line profile analysis, which has been complemented by transmission electron microscopy (TEM) observations. Results of these investigations show that the bulk ultrafine-grained microstructure with high dislocation density produced by ECAP has strong influence on the precipitation process, resulting in high strength in both alloys.