Abstract
The aim of experimental part was to study the influence of Si and Fe on precipitation, recrystallization response, size and formation of secondary phases in the alloys. The hardness and electrical conductivity measurements and light metallography observations were carried out after one- and two-step precipitation annealing. The density of precipitates in all alloys was lower and the primary phases were much coarser in the surface regions of the 2 mm sheets than in the middle. The differences in hardness, electrical conductivity and the microstructure between one- and two-step annealing were only very small. But the two-step precipitation annealing procedure led to the same or lower decrease of the particle density during annealing. Small equiaxial grains were formed in the alloys with Si addition. Except Al-Mn-Zr, the alloys without Si (Al-Mn and Al-Mn-Zr-Fe) showed long recrystallized grains in the surface regions of the sheets. Only the Al-Mn-Zr alloy showed a cold-worked microstructure in the whole cross section of the sheet after the entire one- or two-step annealing procedures. Therefore, Si and/or Fe additions degrade the recrystallization resistance of the Al-Mn alloy with Zr addition and their amount in the commercial alloys should be reduced.

Key words
aluminium alloys, microstructure, precipitation, resistance to recrystallization, microhardness test, electrical conductivity

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