Shumei Wang*, ShanShan Chen*, Kenji Matsuda** ,
Tokimasa Kawabata**, Junya Nakamura***, Susumu Ikeno****, Koji Kawakita*****, Hidetoshi Takagi*****,
Tomokazu Yamashita*****
*Graduate School of Science and Engineering for Education, University of Toyama
**Graduate School of Science and Engineering for Research, University of Toyama
***Graduate School of Environmental Studies, Tohoku University
****Hokuriku Polytechnic College
*****Sankyo Materials Inc.,
The effect of Mn or Fe on the age hardening behavior of Al-Mg-Si alloy was investigated using hardness test and transmission electron microscopy. 8 alloys were used for this work and their chemical compositions were shown in
Table 1. Figure 1 shows the variation of the micro Vickers hardness for the alloys aged at 473 K, which is plotted as a function of aging time. The peak hardness of 0.05Mn, 0.1Mn, 0.05Fe and 0.1Fe alloys is higher than that of the base alloy. The peak hardness of the alloys with small content of Mn or Fe are higher than that of the base alloy; the peak hardness of the alloy with 0.2at.%Fe is similar to that of the base alloy but the peak hardness of the alloy with 0.25at.%Mn is lower than that of the base alloy. The precipitates in Mn- or Fe-addition alloys peak-aged at 473 K are taken by TEM and their bright-field images are displayed in
Fig. 2. There are only needle-shaped precipitates aligning with
100
Al direction for the six alloys. The difference between the number density of the precipitates is attributed to one of the reason for the difference between the peak hardness of the alloys. The typical HRTEM images taken from the cross-section of the precipitates in peak-aged 0.05Mn alloy are shown in Fig. 3. Four typical types of the precipitates are observed in two alloys which were classified according to previous works, namely, the random-type, the parallelogram- type precipitates,
" and
' phases. The dispersoids are not observed in 0.05Mn, 0.1Mn, 0.05Fe and 0.1Fe alloys but observed in 0.25Mn and 0.2Fe alloys. The formation of the dispersoids decreases the age-hardening ability of 0.25Mn and 0.2Fe alloys. Si is expensed to form the dispersoid of AlMnSi or AlFeSi in the alloy with 0.25at.%Mn or 0.2at.%Fe. On the other hand, small Mn or Fe addition enhances the formation of
" phase which is similar to Co- or Ni-addition alloys because Si is not expensed to form such dispersoid in Co- and Ni-addition alloys according to our previous report. It is thought that this will result in the difference of Si in the matrix for the formation of the precipitate.
