Distribution of Mn- and Cr-Containing Dispersoids in Al-Mg-Si-Alloys

摘要

The distribution of Mn- and Cr-containing dispersoids during different annealing of three Al-Mg-Si alloys with different content of Mn and Cr has been studied in detail by light microscope. Heating rate and step-annealing to different temperature have been the external parameters. The tendency to heterogeneous distribution of dispersoids was determined by the image analysis Kontron KS 300, and characterised by the parameter A_e defined as the area empty of dispersoids per unit area. The parameter A_e is a measure of regions empty of dispersoids in the material after a specific heat treatment. A tendency towards a nonuniform spatial distribution of dispersoids was related to the nucleation mechanisms of dispersoids and the microsegregation of the alloying elements after non-equilibrium solidification. It was demonstrate that a prerequisite for a homogenous spatial distribution of dispersoids is a heat treatment procedure that produce an abundant density of beta'-Mg_2Si - needle in a temperature range 250-350 deg C.