Abstract
The aim of this paper is to evaluate the benefit of internal sacrificial layer on automotive brazed heater cores submitted to internal corrosion resistance. In a previous paper (1), a new internal corrosion test called DECLIC has been successfully proposed to simulate cases observed in service. For this test, the synthetic degraded coolant is a neutral mixture containing (6<pH<7) 90 % water, 10 % Ethylene Glycol, 300 ppm chloride and 500 ppm glycollate as Ethylene Glycol degradation product. Furthermore, running cycle is proposed on the basis of the real average car usage. The study leading to define DECLIC test was carried out on the previous generation of heater cores named cross counter flow heater core (CCF heater core), which components are made of known AA4343/AA3003*/AA4343 material. Packaging reduction and performance optimisation lead VALEO to develop a new heater core called I flow heater core (IF heater core) with a reduction material thickness (270 μm vs 400 μm). In order to increase the internal corrosion resistance, components of this new heater core present an internal sacrificial layer on tubes and water tanks (with Zinc as main alloying element). This paper presents results obtained on DECLIC corrosion test on both heater cores (previous generation and new generation) and electrochemical measurement on brazed material, completed by metallographic analysis. Results revealed that the layer containing Zinc was sacrificial due to the galvanic coupling with the core material. Corrosion resistance of the IF heater core, mainly due to the sacrificial layer, in comparison with the CCF heater core, validates the efficiency of this multi-layer material heater core developed by VALEO. The tendencies observed on DECLIC tests suggest that the IF heater core, in comparison with the CCF heater core, could have durability in the field increased by a factor 2.
KEYWORDS – heater core, sacrificial effect, corrosion, circulation test, electrochemistry