“Giant” Chromium Intermetallic Compounds and Stress Corrosion Cracking in Al-Zn-Mg-Cu Alloys

Baba Yoshio, Terai Shiro

doi:10.2320/jinstmet1952.28.2_102

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Other Title

Al-Zn-Mg-Cu合金における巨大クローム金属間化合物について
Al-Zn-Mg-Cu ゴウキンニオケルキョダイクロームキンゾクカンカゴウブツニツイテ
“Giant” Chromium Intermetallic Compounds and Stress Corrosion Cracking in Al-Zn-Mg-Cu Alloys

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Abstract

It is well known that very coarse crystals, up to 2 mm in length, found in large extrusions of 7075 alloy, have been identified as primary crystals of CrAl₇ which grew under semi-continuous casting, and have caused the decrease in fatigue strength. Experiments were carried out to make a study of the prevention of the occurrence of “giant” chromium compounds without decreasing the resistance to stress corrosion cracking in Al-Zn-Mg-Cu alloys. The results obtained are as follows: (1) When the Cr content is less than 0.23% in Al-5.5%Zn-2.5%Mg-1.6%Cu alloy, the occurrence of “giant” chromium compounds is suppressed in commercial practice. However, the addition of >0.3%Mn, >0.3%Fe or >0.05%Ti promotes their occurrence. (2) The addition of Zr 0.1% has no influence on the occurrence of “giant” chromium compounds, and the addition of 0.2 to 0.3%Zr prevents their occurrence. It might be due to the increase in solubility of Cr in the Al-matrix caused by the formation of primary crystals of ZrAl₃ before CrAl₇ at a higher temperature. (3) It is concluded that Al-Zn-Mg-Cu alloy containing both 0.2%Cr and 0.1%Zr is a material having an excellent resistance to stress corrosion cracking, without fear of the occurrence of “giant” intermetallic compounds in industrial production.

Journal

Journal of the Japan Institute of Metals and Materials

Journal of the Japan Institute of Metals and Materials 28 (2), 102-107, 1964

The Japan Institute of Metals and Materials

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