Effect of aging time at low aging temperatures on the corrosion of aluminum alloy 6061

The ISO 11846 Method B is one of the most frequently used corrosion tests to investigate the intergranular corrosion susceptibility of Al‐Mg‐Si(‐Cu) alloys and involves the sample immersion in an aqueous solution containing 30 g/L NaCl and 10 ml/L concentrated HCl for 24 h. Unfortunately, the standard allows for a broad range of parameter variation, for instance the temperature of the test solution and the volume‐to‐surface‐ratio of the solution related to the sample surface area, which causes insufficient reproducibility and reliability of this test method. In the present study, the influence of testing parameter variations within the scope of ISO 11846 Method B on the test results of an almost Cu‐free and a Cu‐containing variant of the 6016 aluminum alloy, both tested in the T4 condition and after a bake‐hardening treatment, was studied in detail. The results show that particularly the volume‐to‐surface‐ratio as well as the surface preparation and the solution temperature significantly influence the test results.

Section: Introductionmentioning

confidence: 99%

Intergranular corrosion testing of 6000 aluminum alloys

Cornejo¹,

Hentschel

Koschel

et al. 2017

“…Therefore, the SHT condition represents the most homogeneous microstructure. This homogeneity in microstructure appears to be the main reason behind the uniform corrosion observed for the SHT samples . There is almost no difference in the potential between the grain interiors and grain boundary.…”

Section: Discussionmentioning

confidence: 83%

Correlation between artificial aging and intergranular corrosion sensitivity of a new Al‐Cu‐Li alloy sheet

Liu

Zhu

Liu

et al. 2016

The intergranular corrosion (IGC) sensitivity of an Al‐3.81Cu‐1.28Li‐X alloy with T6 aging for different time at 150, 175, and 200 °C was investigated. With aging, the alloy potential lowers due to precipitation, accompanied with coarsening and discontinuous distribution of grain boundary precipitates, which contributes to corrosion evolution with aging time. Corrosion mode evolution with aging stage (corresponding to hardness evolution) at aging temperature of 150 and 175 °C follows the following order: pitting and local IGC (early aging), general IGC (under‐aged), local IGC with pitting (near peak‐aged), and pitting (over‐aged). At elevated aging temperature of 200 °C, the corrosion mode evolves much faster. IGC only appears in the intensively under‐aged stage, but the later under‐, peak‐, and over‐aged stage are featured with pitting corrosion. As IGC occurs, its depth is initially increased and then decreased with aging time.

“…Localized corrosion generally forms on the weak spots of the insoluble surface oxide film. However, the corrosion in heat treatable aluminum alloys is affected by chemistry, micro‐defects, such as vacancies and voids, dimensions and distribution of intermetallic precipitates formed during the heat treatments and composition of the electrolyte . The undesirable heat treatments and alloying could be susceptible to intergranular corrosion (IGC) of these alloys …”

Section: Introductionmentioning

confidence: 99%

Corrosion behavior of under‐, peak‐, and over‐aged 6063 alloy: A comparative study

Sekhar

Das

2019

The mechanical property of age‐hardenable Al‐alloys is governed by the state of ageing, which determines the microstructure and consequently, their corrosion behavior which is a vital aspect for a number of applications. This article presents a comparative assessment of corrosion behavior of under‐, peak‐ and over‐aged Al‐Mg‐Si alloy. Corrosion characteristics have been determined via immersion tests in 0.1 M ortho‐phosphoric acid solution and intergranular corrosion (IGC) tests. Corroded surfaces are examined by field emission scanning electron micrographs‐energy dispersive spectroscopy and 3D optical profilometer. The obtained results reveal that the corrosion rate at a specific immersion time as well as the depth of IGC increases in the order for under‐, peak‐, and over‐aged states. Irrespective of the state of ageing, corrosion loss increases linearly but the rate of corrosion decreases rapidly with increasing immersion time. The dominant mode of corrosion in under‐aged alloy is identified as localized pitting, while peak‐aged is highly susceptible to IGC in contrast extensive pitting corrosion is observed for over‐aged alloy. The observed differences in corrosion behavior are explained considering characteristics of precipitates. Formation of β (Mg2Si) in case of over‐aged alloy and presence of inclusions like AlFeMnSi particles are found to accelerate pitting corrosion.