Influence of aging on microstructure, mechanical properties and stress corrosion cracking of 7136 aluminum alloy

Abstract

The microstructure, mechanical properties and stress corrosion cracking (SCC) of 7136 aluminum alloy under T6, T79 and T74 aging treatments were studied and the effects of microstructure on the mechanical properties and SCC were discussed. The results show that the ultimate tensile strength and yield strength of the aging 7136 alloys follow this sequence from high to low: T6>T79>pre-aging>T74. For 7136 Al alloy after T6 aging, the average diameter of the precipitates was (5.7±1.7) nm, and the diameter of 60.7% (number fraction) precipitates was 2–6 nm, leading to a good precipitation strengthening. The K_IC of T74-aging alloy is 38.2 MPa·m^1/2, which is 26.1% more than that of T6-aging alloy and 17.5% more than that of T79-aging alloy. The improved fracture toughness in T74-aging alloy is mainly due to the reduction of the strength difference between intragranular and grain boundary. The SCC resistance of the aging 7136 alloys follows this sequence from high to low: T79 > T74 > T6. After T79 aging, the discontinuous grain boundary precipitates and narrow precipitate free zones were obtained in 7136 alloy, which was beneficial to SCC resistance.

Keywords

7xxx Al alloys / stress corrosion cracking / fracture toughness / precipitate

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