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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. [ABSTRACT FROM AUTHOR]

The effect of the Zn/Mg ratio on microstructures, mechanical properties and corrosion performances of Al-Zn-Mg alloys was studied. Microstructures were characterized using the optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). Tensile tests, intergranular corrosion (IGC) and stress corrosion cracking (SCC) tests were conducted to study the properties. Microstructures results indicated that with the decrease of the Zn/Mg ratio, the recrystallization proportion and the fraction of second phase decreased, while the size of η' (MgZn2) phases in grain interior also significantly decreased. The number density of η' phases in grain interior increased and grain boundary precipitates developed discontinuous distribution with the decrease of the Zn/Mg ratio. These microstructures contributed to the significant improvement of the strength and corrosion resistance. The tensile strength and yield strength increased by 34.1% and 47.4%, respectively, with the Zn/Mg ratio decreased from 11.4 to 6.1. Calculating results indicated that the enhancement of strength mainly contributed from the solid-solution strengthening, grain-boundary strengthening and precipitation strengthening. The intergranular corrosion degree was greatly relieved and the stress corrosion sensitivity index decreased from 0.031 to 0.007 with the Zn/Mg ratio decreased from 11.4 to 6.1. [ABSTRACT FROM AUTHOR]