Pre-Exposure Embrittlement and Stress Corrosion Failure in High Strength A1-Zn-Mg Alloys.
Final technical rept. 12 Jan 74-11 Jan 75,
IMPERIAL COLL OF SCIENCE AND TECHNOLOGY LONDON (ENGLAND) DEPT OF METALLURGY AND MATERIALS ACIENCE
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It has been found that a high purity Al-6Zn-3Mg alloy becomes embrittled if pre-exposed to moist gases prior to tensile testing. The degree of embrittlement increases with the time of pre-exposure and with the temperature and relative humidity of the pre-exposure environment. The alloy is most sensitive to embrittlement when solution treated at 475C but this sensitivity can be reduced considerably if the surface film formed at 475C is removed by electropolishing. The embrittlement is not strain rate sensitive and the ductility of the pre-exposed alloy cannot be recovered by storing unstressed in dry air or in vacuo. However, the ductility of embrittled specimens can be fully restored if tensile testing is carried out under vacuum. If 1.7 copper or 0.14 chromium are added to the high purity alloy the rate of embrittlement is reduced and is even more reduced in the commercial 7075 alloy.
- Properties of Metals and Alloys