Abstract
The effects of different Zn/Mg ratios on the microstructure, mechanical properties and resistance of stress corrosion cracking of peak-aged 7005 aluminum alloy were investigated. It was found that the Zn/Mg ratio played a very important role in controlling the aging time, the electrical conductivity of the hardness peak point and the resistance of stress corrosion cracking of the alloy. With the increase of Zn/Mg ratio (wt. %), the time taken by the alloy to achieve the peak hardness value gradually increases aging at 120 °C. When the Zn/Mg ratio is in the range from 2.27% to 2.62%, the precipitate phase of the alloy after peak-aged is mainly dominated by smaller disc-like η’ phase and GP I (Guinier Preston) zones, the grain boundary precipitates are slender and continuous and the PFZ (precipitate free zones) is narrow. However when this value is in the range from 3.01% to 4.08%, precipitation phase in matrix of the alloy is mainly composed of short-rod η′ phase and GP II zones, the precipitation phases within the grain boundary are large and distribute intermittently and the PFZ is narrower. The results of SSRT (slow strain rate tests) show that when Zn/Mg ≥ 3.61, the 7005 aluminum alloy at peak-aged has good resistance of stress corrosion cracking in 3.5% NaCl + 0.5% H2O2 aqueous solution. However, when Zn/Mg ≤ 3.01, the strength of the alloy sharply decreases in 3.5% (wt. %) NaCl + 0.5% (wt. %) H2O2 aqueous solution.
Highlights
7005 aluminum alloy is widely used in rail transportation and aerospace industry due to its light weight, high strength, good deformability, and good weldability [1,2,3]
Existing literature studies have shown that the poor resistance of 7xxx aluminum alloy series to stress corrosion cracking (SCC) has been overcame using it in over-aged state (T7), which reduces its yield strength about 10–15% comparing to the T6 condition
H2 O2 aqueous solution, the resistance of stress corrosion cracking of alloy gradually increased with the increase in Zn/Mg ratio. These results indicate that there is a correspondence relation between the Zn/Mg ratio and the resistance of stress corrosion cracking of alloy at peak-aged state
Summary
7005 aluminum alloy is widely used in rail transportation and aerospace industry due to its light weight, high strength, good deformability, and good weldability [1,2,3]. In terms of the heat treatment process, such as the retrogression and re-aging (RRA), low-temperature pre-aging (LPA), and non-isothermal aging (NIA), have been developed. These above mentioned heat treatments are complicated, but it decreases the part of the yield strength of the alloy [4,5,6,7,8]. Both of the composition and the heat treatment system are key factors affecting the mechanical strength and stress corrosion resistance of the alloy [9,10,11,12]. It is very meaningful to study the relation between the alloy
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