Double Aged Research Articles

The Microstructure Evolution and Electrochemical Corrosion Behavior of 7A46 Aluminum Alloy in Different Quenching Conditions.

The quenching condition of aluminum alloy can affect the mechanical property and corrosion resistance of the profile. This paper is aimed at the low quench sensitivity of aluminum alloys. Scanning electron microscopy and transmission electron microscopy were used to analyze precipitate behaviors of the 7A46 aluminum alloy under different isothermal cooling conditions and microstructure evolutions of quench-induced precipitations. The effect of the different isothermal time on the corrosion resistance of the alloy, and the relationship between microstructure and corrosion resistance after quenching were revealed through electrochemical impedance spectroscopy and potentiodynamic polarization tests. Results show that corrosion sensitivity of the quenching-aged alloy is much higher than that of the double-aged (DA) alloy, and the corrosion resistance of the quenched alloy decreases firstly and then increases. Due to the high density of the matrix precipitates, the increased content of the impurity element, the discontinuity of the grain boundary precipitates and the widening of the precipitates free zone, the most serious degree of corrosion performance among the quenched alloys is 295 °C at 800 s, and the self-corrosion potential and self-current density is −0.919 V and 2.371 μA/cm2, respectively.

Ａ１−Ｌｉ系合金８０９０厚板の二段時効による破壊じん性の改善

The short-transverse fracture toughness behavior of aluminum-lithium alloy 8090 plate was investigated by using a CNSB (chevron notched short bar) specimen. The fracture toughness KQVM was reduced with a progress of the first-step aging. The double-aged (DA) alloy, which was subjected to the initial underaging (UA2) at 433K followed by the second-step aging at a higher temperature for a short time, exhibited a fairly improved KQVM and a superior strength-toughness balance in comparison with the single-aged alloy, good enough to satisfy the toughness requirement in aircraft design, KQVM/σys≥2.5√mm, where σys is yield strength. The increase in toughness by DA treatment is attributed to the relaxation of intense slips due to dissolution of shearable δ' phase and growth of δ'-PFZ width, leading to the inhibition of intergranular fracture.

Stress corrosion cracking susceptibility and some electrochemical characteristics of Inconel X-750 in lithiated water at 350°C

The stress corrosion cracking (SCC) susceptibility of Inconel X-750 in the as-received (AR) and double aged (DA) conditions was investigated by the slow strain rate test (SSRT) in lithiated hydrogenated water at 350°C. The results showed that the DA condition was more susceptible to SCC than the AR one. Potentiodynamic polarization and AC impedance tests showed that the DA condition was characterized by higher dissolution rate and a lower tendency to passivation than the AR one.