development of 7020 al -al2o3 composite by atomization

Dissertant

Khalaf, Ali Faris

University

University of Technology

Faculty

-

Department

Department of Materials Engineering

University Country

Iraq

Degree

Ph.D.

Degree Date

2008

English Abstract

A laboratory scale assembly based upon atomization principle was indigenously designed, constructed and then used for the preparation of Al (alloy 7020)-based composite samples reinforced with alumina particles of different percentages of 5wt %, 7wl % and 10wt %. Observations, measurements, and analyses were conducted by using various testing techniques, These include optical microscopy, XRD, XRT\ hardness and electrochemical corrosion.

With such approach, good understanding of the microstructure, AI2O3 concentration effects, Lemperature changes, and other governing physical parameters have been established. To complete the scope of the present experimental results, the assembly was also operated in the stir-casting mode throughout a proper replacement of an apparatus designed and locally constructed for such a purpose. Observations with the optical microscope have shown coarse-grained with dendrite structures for the stir-casted samples, while those prepared by atomization technique have experienced fine grains with no dendrites under high cooling rates.

Alumina particles have exhibited homogenous distributions in all samples prepared by both techniques.

Moreover, image analyses via optical microscopy have demonstrated close agreements with the experimental results based on volume fraction calculations. With the XRD analyses, a-Al203 phase was identified and the 20 values confirmed the existence of Al2O3 in the 10 % aluminum matrix composites. Investigations for the effect of magnesium (Mg) metal which was used as a wetting agent on the interaction of Al-matrix with the A1203 particles were carried out by the XRF technique.

Such interaction rate imposed less Mg Higher hardness values were observed for the atomized samples, as compared with those prepared by stir-casting.

However the hardness values were found to be enhanced with increasing concentration of Al2O3 particles in the alloy matrix. For both groups of samples the effects of temperature, A1203 concentration, and anodizing process were thoroughly studied with particular emphasis on the corrosion localization over sample structures.

In this context, the corrosion rate was found to increase as the temperature was nominally raised from 30C to 38c and 45C for the 10 % stir-cast samples in 3.5% Nacl solution. At a temperature of 30C, the corrosion rate was found to rise with increasing concentration of AI2O3 particles for the given atomized samples.

Nevertheless, stir casting samples demonstrated slightly higher corrosion rate than those prepared by atomization due to their structural behavior, It was also found that the anodizing processes resulted in higher corrosion resistance when the thickness of the oxide layer exceeded 8 microns. Optical microscopy showed also a profound appearance of corrosion location near the grain boundaries and dendrites in the stir-cast samples.

An appearance of a general corrosion has the main characteristic feature of the prepared atomized structures.

Main Subjects

Physics

Topics

• Mechanical properties
• Aluminum alloys

• APA
• MLA
• AMA

Language

English

Data Type

Arab Theses

Record ID

BIM-305024