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.

On the extraordinary low quench sensitivity of an AlZnMg alloy

The scope of this work was to investigate the quench sensitivity of a high-purity wrought aluminum alloy Al6Zn0.75 Mg (in this work called 7003pure). This is compared to a similar alloy with the additions of Fe, Si, and Zr at a sum less than 0.3 at.% (in this work called 7003Fe,Si,Zr). Differential scanning calorimetry (DSC) was used for an in situ analysis of quench induced precipitation in a wide range of cooling rates varying between 0.0003 and 3 K/s. In 7003pure, three main precipitation reactions were observed during cooling, a medium temperature reaction with a distinct double peak between 325 and 175 °C and a very low temperature reaction starting at about 100 °C. An additional high temperature reaction related to the precipitation of Mg2Si starting at 425 °C has been observed for 7003Fe,Si,Zr. In terms of hardness after natural as well as artificial aging, alloy 7003pure shows a very low quench sensitivity. Hardness values on the saturation level of about 120 HV1 are seen down to cooling rates of 0.003 K/s. The as-quenched hardness (5 min of natural aging) shows a maximum at a cooling rate of 0.003 K/s, while slower and faster cooling results in a lower hardness. In terms of hardness after aging, 0.003 K/s could be defined as the technological critical cooling rate, which is much higher for 7003Fe,Si,Zr (0.3–1 K/s). The physical critical cooling rates for the suppression of any precipitation during cooling were found to be about 10 K/s for both variants.

Avials, history of creation and overview of future outlook

Scientific domestic and foreign literature touching the field of Al – Mg – Si wrought aluminum alloys are reviewed, the history of appearance of the most common brands is described. It is shown that the development of alloys was proceed gradually advancing their chemical composition along the quasi-binary Mg/Si = 1.73 сross -section in the direction of increasing concentration of just Mg and Si, and the strength of last modern brands was provided by additional alloying, primarily copper, the content of which can reach 1-1.4%. The influence of alloying elements on microstructure, mechanical and corrosion properties of alloys is described, features of their heat treatment, factors of maximum strengthening and susceptibility to intergranular corrosion are revealed. Attention is focused on the key role of the Mg/Si ratio, transition metals, Cu, Cr and Mn first of all, in the formation of balanced properties, since the positive effect of these elements on increasing the strength and the recrystallization temperature is often offset by the negative impact on intergranular corrosion and quench sensitivity. It is shown that in low-alloyed Al–Mg–Si alloys the strength premises Mg/Si≈1 and the premises for high-end corrosion resistance Mg/Si≈2 are occurred simultaneously. Alongside an increase of the absolute content of Mg and Si in alloys, alongside an increase of alloying degree with other strengthening elements, it is impossible to simultaneously fulfill both of these premises; therefore, one has to look for a reasonable compromise between strengthening, decreasing the technological plasticity and corrosion resistance of alloys. One of the effective ways to reach such a compromise is multi-stage regimes of artificial aging. The prospects of microalloying with Sc and Ca able to form with aluminum nanoscale intermetallic phases of hardening are outlined. Keywords: avials, semi - finished products, alloying system, transition metals, aging, mechanical properties, intergranular corrosion.