| Budget Amount *help |
¥3,900,000 (Direct Cost: ¥3,900,000)
Fiscal Year 1985: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 1984: ¥2,900,000 (Direct Cost: ¥2,900,000)
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| Research Abstract |
The purpose of this investigation is to present the development of new weldable Al-Zn-Mg alloy with high resistance to stress corrosion cracking by means of additions of minor alloying elements.
The stress corrosion cracking of Al-Zn-Mg alloy occurs by the pitting or corrosion. In this investigation, the measurement of pitting potential was carried out as the evaluation of corrosion resistance.
As the new alloy, Al-4.5%Zn-1.2%Mg alloys separately added 0.2%Cr 0.5%Mn,0.05%Ti and 0.2%Fe-0.1%Si, and then Al-4.5%Zn-1.2%Mg alloy with various contents of Cr,Zr and Cu up to 1 % in order to improve the corrosion resistance were prepared.
The effect of the minor alloying elements on aging characteristics and corrosion resistance was studied by means of metallurgy and electrochemistry by anodic polarization characteristics. The results were summarised as follows.
1. The addition of Cu or Cr to the Al-4.5%Zn-1.2%Mg alloy causes the increase of the pitting potential. But the pitting occurs predominantly at the grain boundaries above 0.2%Cu or 0.2%Cr. Therefore,addition of 0.2%Cu or 0.2%Cr is effective ,concerning the stress corrosion cracking.
2. The addition of 0.05%Ti,0.2%Fe-0.1%Si or 0.5%Mn is effective to inhibit the grain growth, but hardly affect the pitting potential.
3. The Zr addition up to 0.2% to the Al-4.5%Zn-1.2%Mg alloy affects the refining of the grain size,but the Zr addition above 0.5% causes the reduction of corrosion potential and causes the stress corrosion cracking.
4. On the basis of the results above mentioned, the additions of 0.05%Ti,0.2%Cr,0.5%Mn,0.2%Fe-0.1%Si,0.2%Zr and 0.2%Cu to the Al4.5%Zn -1.2%Mg alloy are effective to improve the stress corrosion cracking and corrosion resistance of the weld heat affected zone.
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