All technological properties of materials are directly connected to their microstructure. Among these properties are their strength and deformation characteristics, their wear and high temperature behaviour, and also their corrosion behaviour and the failure behaviour under fatigue loads. Some of these properties can be changed dramatically by slight changes in the microstructure.
Apart from metallographic equipment with different optical microscopes a scanning electron microscope and a high resolution 300 kV transmission electron microscope are available for micro-structural investigations. Typical operational areas of the electron microscopic devices are the investigations of fracture surfaces, the determination of chemical concentration profiles and extensive phase analyses.
At present microstructural investigations of aluminium alloys are performed particularly in connection with friction stir welding. The structure in the welding seam and in its direct surrounding is very strongly changed by the welding process. By correlation and by skilful choice of the welding parameters attempts are made to positively affect the mechanical characteristics and the corrosion characteristics of the welding seams through its microstructure.