Effect of simulated brazing on the microstructure and corrosion behavior of twin roll cast AA3003

Abstract

Aluminium alloy (AA) 3003 is widely used as fin and tube material in heat exchangers. In these heat exchangers the tube and fin material are brazed together by means of an AA4xxx alloy. In this work, the effect of a simulated brazing step on the microstructure and corrosion behaviour of a twin roll casted (TRC) AA3003 was studied. In particular, the effect of simulated brazing on the corrosion properties of the centre line segregation (CLS) of alloying elements and the interaction of the intermetallic particles with the surrounding matrix is explored. It is shown that the cross sections are significantly more active than the surface of the TRC AA3003, revealing the importance of the CLS on the corrosion behaviour. Furthermore, it is shown that the number of pits and their depths decreased considerably on the exposed cross sections after simulated brazing, especially near the CLS. Scanning Kelvin probe force microscopy (SKPFM) measurements show that after the simulated brazing step the Volta potential difference between the intermetallic particles and the matrix reduced significantly. This change in the Volta potential could be caused by the slight increase of Si content in the matrix.

Methods—On the Application of Ambient Scanning Kelvin Probe Force Microscopy to Understand Micro-Galvanic Corrosion Phenomena: Interpretation and Challenges

“…Furthermore, some published studies can be found in which topography maps acquired simultaneously or associated with relevant potential maps are neglected and not shown when presenting SKPFM results. 2,4,6,51,[61][62][63][64] Even though the most pertinent information concerning corrosion studies is contained in the CPD maps, this practice is highly discouraged. Topography images are relevant to visualize correlations between topographical features and Volta potential differences accurately.…”

“…Several examples of histogram analysis of Volta potential data can be found in previous studies. 28,56,61,62,[69][70][71][72][73][74][75] The use of histograms not only allows the calculation of the most representative potential values characterizing the different phases mapped (and their Volta potential differences), but also provides a measure of their individual potential distributions through their standard deviations (calculated from the FWHM -full width at half maximum-of the multinomial peak simulation of the histogram). 62,[73][74][75] An example of a multinomial peak de-convolution analysis of the histogram acquired from a CPD image is shown in Fig.…”