The Effect of Grain Structure on the Stress Corrosion Resistance Al-Zn-Mg-Cu Alloys.
ROYAL AIRCRAFT ESTABLISHMENT FARNBOROUGH (ENGLAND)
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Three alloys, Al-6Zn-2.5Mg-1.5cu, Al-6Zn-2.5Mg-1.5Cu-0.15Zr and Al-6Zn-2.5Mg-1.5Cu-0.17Fe-0.15Cr-0.11Mn were produced as 37mm plate in the T6 condition. The stress corrosion resistance, fracture toughness and tensile properties of the alloys were determined to identify the effects of the grain refining elements, Zr, Cr, Fe and Mn on these properties. A special processing treatment, involving extensive precipitation and warm working, was also applied to pieces of plate to produce an extensively recrystallised structure, with a small grain size, for comparison with the coarser structures of the conventionally worked alloys. The results indicated that the alloy containing Fe, Cr and Mn had the highest stress corrosion resistance and strength but the lowest fracture toughness. The addition of 0.15 Zr to the quaternary alloy slightly improved the tensile strength and stress corrosion resistance but had no effect on fracture toughness. However this addition of Zr markedly improved the hot workability of the alloy and increased its tensile ductility. Special processing and working at 250 C was beneficial to the stress corrosion resistance of the quaternary alloy but detrimental to that of the other two alloys containing Zr or Fe, Cr and Mn. It was concluded that, in these Al-Zn-Mg-Cu alloys, a recrystallised grain structure has a low stress corrosion resistance and that inhibiting recrystallisation increases stress corrosion resistance. Author
- Properties of Metals and Alloys