Efeito do envelhecimento artificial na microestrutura e resistência à corrosão das ligas 6351 e 6005A

Abstract

In the last decades, aluminum alloys have undergone an intense process of innovation and evolution in terms of improving mechanical properties through modifications in chemical composition and heat treatments. In this context, the 6005A and 6351 alloys were developed as part of the 6XXX series, classified as medium-strength alloys, with their primary hardening mechanism being artificial aging heat treatment. These alloys find applications in structural uses such as civil construction, ship and automobile structures, aircraft fuselage, railways, and variously shaped components. The objective of this study was to carry out solubilization heat treatments on the 6351 and 6005A alloys at 580°C and 540°C for 1 hour, respectively. Additionally, aging heat treatments were performed at 180°C for 1 hour, 2 hours, 3 hours, 4 hours, and 6 hours. It was observed that the proposed heat treatments did not completely dissolve the intermetallic phases β-AlFeSi and α-AlFeMnSi in both alloys, in addition to the Q-AlMgSiCu phase, which was only observed in the 6005A alloy. However, the aging treatments precipitated refined particles of the Mg2Si phase, leading to an increase in hardness with longer aging times. The highest hardness values were 92.8 HRB for the 6351 alloy and 67.3 HRB for the 6005A alloy after 6 hours of aging. In the tests of potentiodynamic linear polarization, it was observed that the highest corrosion potentials were -0.66V and -0.95V for the 1-hour aged 6351 alloy and the 6-hour aged 6005A alloy, respectively. The passivation current density did not show significant variation for the alloys under the given heat treatment conditions, with an average value of around 0.29 A/cm², indicating that the heat treatments did not affect the passivation capability of the alloys.