The effect of temperature on the sequence of hardening precipitates in Al-1.15 Mg2Si-0.34Cu (wt %) balanced containing Cu and Al-1.14Mg2Si-0.34Cu balanced containing Cu with Si in excess alloys has been investigated by hardness measurement (HV), differential Scanning calorimetry (DSC) and Transmission electron microscopy (TEM) techniques. The values of the hardness number which corresponding to the hardening precipitated particles in the alloy containing Si in excess are higher than that in the alloy without Si. The results showed that, the difference in the hardening precipitation peaks positions may match the fact that, the excess Si increases the density of β‶ metastable phase and also, reduces the Mg/Si ratios in the early stage of GP zones and co-clusters formation. After the complete formation of the metastable needle shaped precipitates β‶ is taken place the strengthening of the alloy would take place as a result of the formation of the semi-coherent rod shaped precipitates β‵ and/or Q‵ phases.
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