Development of an Aluminum Brazing Sheet Product with Barrier Layer for High-Performance Automotive Heat Exchangers

A high-strength aluminum brazing sheet product has been developed for automotive heat exchangers. It consists of commercial Al-Si clad, newly designed Al-Mn-Cu-Mg core, and pure aluminum barrier between the clad and core. The microstructure, mechanical properties, corrosion resistance, and braze-ability were investigated and compared with regular brazing sheets without barrier. The newly designed Al-Mn-Cu-Mg alloys are much stronger than commercial Al-Mn-Cu core alloys and the high strength is maintained up to 573.15 K (300 °C). However, liquid–solid interaction occurs extensively during brazing when the Al-Si clad contacts the Al-Mn-Cu-Mg core directly, resulting in degrading of mechanical properties and corrosion resistance. The barrier provides a physical separation between the clad and core, preventing not only the liquid–solid interaction, but also the solid diffusion of Si from clad to core and Mg from core to sheet surface. The accumulation of Si and Mg in the barrier leads to a high population density of Mg₂Si precipitates, acting as a sacrificial band to delay the through-thickness corrosion. Meanwhile, the low Mg level in the sheet surface ensures high braze-ability for commercial flux brazing processes. The new sheet product is therefore suitable to high-performance automotive heat exchangers, especially the ones that may serve at temperatures above 473.15 K (200 °C).