The influence of different types of precipitation on the corrosion behavior was investigated in three aluminum-siliconmagnesium alloys. The microstructures of the alloys were studied through optical (OM) and scanning electron microscopy (SEM). The structures consisted of an α-Al solid solution matrix, Si eutectic crystals, secondary phases AlFeSi and AlMgFeSi (Chinese script), as well as Mg₂Si. The corrosion behavior was examined with the use of a potentiodynamic polarization test followed by a SEM surface analysis. The results indicate that all the analyzed samples were in the passive state and AlSi10Mg was less reactive in the corrosive environment.

A study has been undertaken to reveal the microstructure, mechanical and creep properties of two Mg-4Y-3RE and Mg-3Nd-1Gd magnesium alloys. The relationship between the ageing parameters, microstructure, mechanical and creep properties was specified. Structure investigations showed that the mechanical properties maximum during the ageing at 200°C/16h (Mg-3Nd-1Gd alloy) and at 250°C/16h (Mg-4Y-3RE alloy) resulted from the formation of fine beta;ldquo; and β” precipitates in the α-Mg solid solution. Further ageing led to decrease of the mechanical properties due to formation of β1 and β phases in Mg-4Y-3RE alloy or only β phase in Mg-3Nd-1Gd. The creep tests of the Mg-3Nd-1Gd alloy at temperature 200°C in the stress range 90-150MPa show the larger creep strain and steady-state creep rate than the Mg-4Y-3RE alloy

The paper presents the results of DSC and microstructural investigations of Elektron 21 magnesium alloy in as cast condition and after solution hardening. Elektron 21 is a magnesium based casting alloy containing neodymium and gadolinium for used to at 200°C in aerospace application. The solution heat treatment was performed at 520°C/8h/water. Ageing treatment was performed at different temperatures 200, 250, 300 and 350°C, then quenched in air. The microstructure of Elektron 21 in as cast condition consists of primary solid solution α -Mg grains with eutectic α-Mg + Mg3(Nd,Gd) phase and regular precipitates of MgGd3 phase. After DSC investigations three exothermal signals has been observed. First exothermal signal at ~170÷245°C assigned to an undifferentiated formation of the metastable phases β” and β’ and the second one at ~280°C corresponded to the formation of a stable β (Mg3Nd) phase. The last signal at ~300°C was connected to the formation of Mg41Nd5 phase. Regular precipitates of MgGd3 phase have been also observed. TEM investigation confirmed that the Elektron 21 alloy precipitate from the solid solution according to the sequence of the following phases: α–Mgβ”β’β(Mg3Nd)Mg41Nd5