Transmission electron microscopy studies of dispersoids and constituent phases in Al-Mn-Fe-Si alloys

3xxx aluminium alloys are used among others in packaging, architectural applications and heat exchangers. Both dispersoids and constituent phases are very important in this alloy system. The size and distribution of the dispersoids have a strong influence on the deformation, the recovery and recrystallisation behaviour and final mechanical properties of the 3xxx Al alloys. Also the constituent phases influence recrystallisation, grain size, texture and mechanical properties. In this thesis dispersoids and constituent phases in 3xxx Al alloys were studied, using transmission electron microscope (TEM) techniques as the main tools for the investigations. The alloys studied here were direct chill-cast 3xxx aluminium alloys with varying material composition. They were studied after various low temperature homogenisations. Constituent phases extracted from the Al matrix were studied with respect to type, lattice parameters, chemical composition and morphology in alloys with various composition. Al6(Fe,Mn) was found to be the most prominent constituent phase in the alloy with a low Si content. Orientation relationships (ORs) of constituent particles with relation to Al matrix were investigated for Al6(Fe,Mn) and α-Al(Fe,Mn)Si constituents. The OR between the Al matrix and the Al6(Fe,Mn) constituent was determined to be [-1-1-2]c // [-11-1]Al , (33-3) c // (0-2-2)Al . This OR is consistent with the OR of Al6(Fe,Mn) dispersoids. α-Al(Fe,Mn)Si constituent particles in the Si rich alloy were found to have various possible orientations. The main focus of this thesis is the study of α-Al(Fe,Mn)Si dispersoids. How the precipitation of α-Al(Fe,Mn)Si dispersoids influences the hardness and tensile strength in alloys were systematically investigated. The evolution of density, size and volume fraction of the α-Al(Fe,Mn)Si dispersoids when varying the annealing time, the temperature and the alloy composition was quantitatively studied by conventional TEM and electrical measurements. A hardening effect from the dispersoids was revealed. The hardening effect increases with increasing Mn and Si contents in the alloys. A high number density of relatively small dispersoids are beneficial for the hardness. For some applications of the 3xxx alloys this hardening during low temperature annealing is of significant importance for the further process. The α-Al(Fe,Mn)Si dispersoid phase is a cubic icosahedral quasi crystal approximation phase. Investigations of quasi crystal approximant