K. Matsuda et al., Changes of microstructure in Al-Mg2Si alloys containing several Mg2Si contents during heating, J JPN METAL, 65(5), 2001, pp. 409-413
Differential scanning calorimetry (DSC) measurements and high resolution tr
ansmission electron microscope (HRTEM) observations were performed in order
to confirm the precipitation sequence of Al-Mg2Si alloys containing of 0.6
, 1.0 and 1.6 mass%Mg2Si during heating. Peaks in the DSC curves were clear
ly observed to form when the Mg2Si content was increased from 0.6 to 1.6 ma
ss%. Exothermic peak A, endothermic peak B, and three exothermic peaks C, D
and E appeared in the Al-1.0 mass %Mg2Si alloy upon heating from room temp
erature. Peak C was the highest exothermic peak among them. It was difficul
t to detect clear peaks in the DSC curve of the Al-0.6 mass%Mg2Si alloy. Ne
edle-shaped precipitates were observed at 557 K, corresponding to peak C in
the Al-1.0 mass%Mg2Si alloy, and coarsened with increasing temperature. Th
ere was far less precipitate in the Al-0.6 mass%Mg2Si alloy, and the precip
itates were coarser. The highest density of random-type precipitate occurre
d in the temperature range of 493 K to 557 K in the Al-1.0 mass%Mg2Si alloy
, as determined by HRTEM. Many parallelogram-type precipitates occur at 557
K, and the beta ' phase appears at temperatures higher than 580 K. This te
ndency is similar to that of the Al-1.6 mass%Mg2Si alloy. The precipitation
sequence in the Al-0.6 mass%Mg2Si alloy is similar to that in the Al-1.0 a
nd 1.6 mass%Mg2Si alloys, however there is temperature range in the Al-0.6m
ass%Mg2Si alloy where the abundance of parallelogram-type precipitate equal
s that of the beta ' phase. No beta " phase was observed in any of the allo
ys. The hardness of alloys was greatest at temperatures corresponding to th
e respective peaks in the DSC curves in Al-1.0 and 1.6 mass%Mg2Si alloys, w
hich is in agreement with the temperature at which the density of random-ty
pe precipitate is highest.