Bogusława Adamczyk-Cieślak

The Microstructure of AlSi7Mg Alloy in as Cast Condition

The complex microstructure of as-cast AlSi7Mg alloy has been investigated. Microstructure observations were done using light microscopy, scanning electron microscopy and transmission electron microscopy. Chemical composition of the microstructure constituents was investigated by means of energy dispersive spectrometry, conducted both during SEM and STEM investigations. Selected area diffraction was used to identify the phases in the alloy. Microstructure of the alloy in the as-cast condition consists of Al-Si eutectic and intermetallic phases in the interdendritic regions. These are: Mg2Si, α-AlFeMnS, β-AlFeSi and π-AlFeSiMg phases. What is more, number of fine precipitates were found within the α-Al dendrites. Only the occurrence of U1 (MgAl2Si2) phase has been confirmed.

Texture Development in a Model Al-Li Alloy Subjected to Severe Plastic Deformation

The texture of Al – 0.7 wt. % Li alloy processed by two different methods of severe plastic deformation (SPD) has been investigated by X-ray diffraction, and analyzed in terms of the orientation distribution function (ODF). It was found that severe plastic deformation by both Equal Channel Angular extrusion (ECAE) and Hydrostatic Extrusion (HE) resulted in an ultrafine grained structure in an Al – 0.7 wt. % Li alloy. The microstructure, grain shape and size, of materials produced by SPD strongly depend on the technological parameters and methods applied. The texture of the investigated alloy differed because of the different modes of deformation. In the initial state the alloy exhibited a very strong texture consisting of {111} fibre component. A similar fibrous texture characteristic was also found after HE whereas after the ECAE the initial texture was completely changed.

Mechanical Properties of Ultra-Fine Grained Al-Li Alloys

The results obtained in the present study reveal the effect of equal channel angular extrusion (ECAE) on the grain size and mechanical properties of Al-Li alloys. During 8 passes of ECAE process, coarse grain microstructure in the initial state transforms into ultrafine grained. The final grain size depends on both total strain applied and Li content in the alloy. Due to the grain refinement the microhardness and yield stress increase by 100%. During compression deformation, the coarse grain alloys exhibit continuous hardening, whereas in the ultrafine-grained alloys, a stagnation of work hardening at the beginning of compression deformation is observed. This behaviour is related to the dynamic recovery of the severely deformed microstructure.

Recrystallization and Grain Growth in Al-Li Alloys Subjected to Severe Plastic Deformation

Equal channel angular extrusion (ECAE) was used to obtain ultrafine grain structures in two aluminium- lithium alloys. The specimens were subjected to severe plastic deformation up to strain value of 9,2 at room temperature. After ECAE deformation, the grain size was reduced from an initial value of 300 µm to 1 µm. The main purpose of this study was to examine the recrystallization characteristics of ECAE treated specimens at temperatures of T = 0,5 and T = 0,7 Tm. At each temperature the specimens were heated for 1, 10, 100 seconds. The microstructure, texture and microhardness were examined in the as-deformed condition and after the annealing. The TEM observations indicate that in the Al-0.7 wt. % Li and Al-1.6 wt. % Li alloys, recrystallization has a continuous character. The microhardness results show that the lithium content increases, in an essential way, the mechanical properties of the alloys after severe plastic deformation and subsequent annealing. During ECAE process, a well pronounced texture with the orientation of the (441)[ 12 4 ], (145)[ 7 31] and (321)[ 3 4 6 ] types are formed within about ¼ volume of the material. After the annealing the grains acquire orientations other than those observed typically in these alloys when deformed by classical straining techniques followed by recrystallization.

Ultra-Fine Grain Structures Of Model Al-Mg-Si Alloys Produced By Hydrostatic Extrusion

Microstructure and mechanical properties were studied in model Al‐Mg‐Si alloys (Al‐1 % Mg‐0.8% Si and Al‐0.5% Mg‐0.3% Si‐wt %) deformed by hydrostatic extrusion (HE) to strains of 1.4 and 3.8. In these alloys the different percentage of two hardening second‐phase precipitates (Mg2Si and Si) were observed. The microstructure was characterized by transmission electron microscopy and optical microscopy. The microstructure of the alloys in the initial state was built of coarse grains of an average diameter of ∼30 rim. The refined microstructure was examined qualitatively and quantitatively using the stereological method and a computer image analysis. The deformation‐processed structures evolved very rapidly, forming ultrafine grained (UFG) materials with grains of about 0.4 μm. In addition, the grain refinement in the HE‐treated materials has a substantial effect on their properties, such as the mechanical strength and micro‐hardness which increase significantly. It has been found that, after e = 3.8 in the A...