51316-7505-Effect of Long-Term Heat Treatments on The Corrosion of High-Strength Al-Mg-Si-Cu Alloys

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Product Number: 51316-7505-SG

ISBN: 7505 2016 CP

Author: Daniela Zander

Publication Date: 2016

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Intergranular corrosion (IGC) can occur in most types of aluminum alloys; however high-strength alloys which achieve their mechanical properties through special heat treatments such as the 6xxx series display a higher susceptibility to corrosion. The peak-strength condition usually obtained via artificial aging (T6) is frequently accompanied by a maximum IGC susceptibility and many investigations on the correlation between artificial aging and IGC susceptibility have been conducted during the last decades. However microstructural changes influencing the corrosion properties do not only occur during specific heat treatments but may also arise during service. In automotive applications particularly near-engine components may suffer long-term heat impact that may cause appreciable over-aging of the microstructure. As a worst case scenario the automotive industry specifies a long-term heat impact in near-engine regions of up to 150°C for 1000 hours. During this over-aging process the precipitations coarsen and their impact on precipitation strengthening decreases. In addition to the decrease of the mechanical properties the microstructural changes during over-aging influence the corrosion properties as well. However so far hardly information is presented in the literature about the correlations between long-term heat treatments and the corrosion properties.In recent investigations the effects of long-term heat treatments on the corrosion properties of a technical Al-Mg-Si-Cu alloy was investigated in detail. Based on peak-aged samples over-aging was conducted for up to 1000 hours at 150°C with removing one sample each three or four days. As corrosion testing the standard ISO 11846 was utilized and corrosion mechanisms were analyzed using scanning as well as transmission electron microscopy.