Influence of multistep aging on the stress corrosion cracking behavior of aluminum alloy 7010

Abstract

The 7000 series, high-strength aluminum alloys are used in aircraft structures because of their high strength to weight ratio.1 Aluminum alloy (AA) 7075 of this series has been used widely for the past few decades and has been researched by several workers.2-4 However, the demand for further improvement in the strength and toughness still exists. Literature review shows that AA7010 was developed to substitute the traditional AA7075.5-6 The low level of iron and silicon impurities in AA7010, when compared to 7075 alloy, leads to higher toughness of the former.7 A small amount of zirconium in AA7010 not only maintains the fine grain structure but also reduces the quench sensitivity of the alloy.8

It is well known that the 7000 series alloys are susceptible to environmental embrittlement. The mechanism is discussed extensively by many authors.7-13 Anodic dissolution and hydrogen embrittlement theories have been proposed to interpret environmental embrittlement of Al alloys. The anodic dissolution theory explains that stress corrosion cracking (SCC) takes place with the preferential dissolution of the grain boundary precipitates.14 On the other hand, the hydrogen embrittlement theory explains that hydrogen accumulates in the dislocations and hinders the dislocation movement and henceforth decreases the ductility.2 Najjar, et al.,15 reported that combined action of anodic dissolution and hydrogen uptake was the reason for SCC in the 7000 series alloys. Scamans, et al.,16 suggested that the magnesium segregation to the grain boundary plays a critical role.