Abstract
The influence of the microstructure on the corrosion susceptibility and mechanism of aluminum sheet was studied. The homogenization annealing treatment results in the segregation of copper on the surface of the re-solidified clad material and the increase of the diffusion depth of Si during brazing. The band of dense precipitates has a higher corrosion potential than clad and core material, and the high density particles in the diffusion zone (40 um<;depth<;70 um) are identified as α-Al(Fe-Mn)Si particles. Thus, the band of dense precipitates are catalytic sites for cathodic reduction reactions. Moreover, the effect of homogenization annealing treatment on the local electrochemical activity and corrosion properties are studied. The results indicate that the band of dense precipitates formed in the diffusion zone in the sample without homogenization annealing during brazing process, which improves the corrosion resistance of the material. Compared with sample with homogenization annealing at the same thickness, the time for the perforation during seawater acetic acid test of the sample without homogenization is longer than that of the homogenization annealed sample.
Highlights
Aluminum alloys are commonly used in automotive applications due to their light weight and excellent physical properties [1]–[4]
According to the Particle Stimulated Nucleation (PSN) theory, these small dispersed particles inhibit the movement of dislocation and sub-grain boundaries, hindering the nucleation and growth of recrystallized grains [14]
(1) Small and dispersed second phase particles in the nonhomogeneous annealing sample inhibit the movement of dislocation and sub-grain boundaries, hinder the nucleation and growth of recrystallized grains, and lead to coarse recrystallization grains
Summary
Aluminum alloys are commonly used in automotive applications due to their light weight and excellent physical properties [1]–[4]. During the complex manufacturing of heat exchanger tubes, the interdependence between the evolution of the microstructure and the processes at each stage become increasingly important. To improve the mechanical properties and corrosion resistance of brazing sheets, it is a good way to optimize components by thermo-mechanical processing [5]–[8]. Microstructural evolution depends on the alloy composition, and on the process conditions to a large extent. Homogenization annealing conditions, one of the important parts of brazing sheets manufacture process, should be carefully considered. Homogenizing heat treatment of the material reduces the concentration of Mn in solid solution and is used to change the size and the distribution of the particles [9].
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