Gradient multilayer aluminium sheets used in automotive heat exchangers
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Gradient multilayer aluminium sheets used in automotive heat exchangers Zhipeng Yuan1,2, Yiyou Tu1,2,*
, Ting Yuan3, Yaohua Huang1,2, and Yunhe Zhang1,2
1
School of Materials Science and Engineering, Southeast University, Nanjing 211189, China Jiangsu Key Laboratory of Advanced Metallic Materials, School of Materials Science and Engineering, Southeast University, Jiangning District, Nanjing 211189, China 3 School of Chemistry and Material Engineering, Changshu Institute of Technology, Changshu 215500, China 2
Received: 23 July 2020
ABSTRACT
Accepted: 17 November 2020
The local electrochemical measurement and corrosion mechanism of the multilayer aluminium sheets (AA4343/AA3xxx/AA4343 and AA7072/AA3xxx/ AA4343) after brazing are determined by a combination of mechanical polishing and work function calculation based on density functional theory. The work functions of (100), (110), and (111) crystal planes of Si and a-Al(Fe,Mn)Si particles which are common in multi-layer aluminium sheets are calculated. The results demonstrate Si and a-Al(Fe,Mn)Si particles are considered to be cathodic with respect to the Al matrix, thus promoting cathodic reactions. The potential differences between the Si and a-Al(Fe,Mn)Si particles with respect to the Al matrix may lead to localized dissolution of the Al matrix. Besides, the microstructure and composition of multi-layered aluminium sheets are studied by optical microscopy, scanning electron microscopy, and glow discharge optical emission spectrometry and compared with those obtained for conventional multi-layer aluminium sheets (AA4343/AA3xxx/AA4343). The presence of the AA7072 layer reduces the outward diffusion of copper. In addition, the AA7072 sacrificial layer exhibits a large potential difference against the core material for a long time, thereby improving corrosion protection.
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Springer Science+Business
Media, LLC, part of Springer Nature 2020
Introduction Aluminum alloys are widely used in automotive applications due to their sufficient corrosion resistance, light weight, excellent physical properties, and Handling Editor: Kyle Brinkman.
Address correspondence to E-mail: [email protected]
https://doi.org/10.1007/s10853-020-05584-5
ease of recycling [1]. Al alloys have become increasingly common in automotive industry for heat exchangers [2]. The commonly used multi-layer aluminium sheets consist of AA3xxx core alloy (Mncontaining) and AA4xxx clad alloy (Si-containing).
J Mater Sci
Corrosion on the water side of the multi-layered aluminium sheets is an extremely critical issue and is a major problem in weight reduction [3]. In the conventional multi-clad aluminium sheets (AA4343/ AA3xxx/AA4343), core materials are prone to intergranular corrosion (IGC), which causes tube perforation, leading to coolant leaking [4]. Si diffused from the AA4xxx clad layer to the AA3xxx core layer after brazing, which enhances this corrosion [5]. The use of conventional multi-clad aluminium sheets (AA4343/ AA3xxx/AA4343) used in automotive applications is limited due to corr
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