Electrochemical and microstructural characterization of multi-clad aluminium brazing sheets

摘要

Aluminium alloys are widely used in automotive heat exchanger applications due to a favourable combination of mechanical and electrochemical properties, such as low density combined with good strength, thermal conductivity and corrosion resistance. Over the years, mechanical assembly of heat exchangers has been replaced by brazing due to benefit of low costs and safety issues. In this study, we investigate the corrosion propagation mechanism across a multi-clad Al alloy brazing sheet as a function of the local alloy composition and microstructure, with and without brazing treatment. Multi-clad structure used was a four-layer sandwich consisting of a modified AA3xxx core alloy, AA4343 brazing clad on both sides and an AA3xxx interlayer on the airside of the sandwich sheet. The polarization behaviour of both as-rolled and brazed sheets was studied as a function of depth using a localized electrochemical cell and GDOES sputtering. The changes in the microstructure caused by the brazing process were observed by scanning (SEM) and transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). The observed evolution of the electrochemical parameters through the material depth was analysed and correlated to the respective microstructural and compositional features. The obtained results were compared to those obtained for a conventional, three-layer alloy product.