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The Effect of Material Selection on the Service Life of All Aluminum Radiator

Modern automobiles are developing in the direction of light weight, high efficiency and economy as a whole. As one of the important components in the automobile heat exchange system, the radiator is responsible for the cooling of circulating water. The update of its structure and materials also follows this principle. Because aluminum has the advantages of light weight, low cost of raw materials, and good heat dissipation performance. At present, aluminum alloy composite materials have been widely used as radiator tube materials due to their high strength, high thermal conductivity and good corrosion resistance.

1. Parameters of full aluminum radiator

The experimental objects are radiators with six different material combinations, including three parts: flat tubes, fins and headers. The flat tubes of A, B and C are non-composite. A is 1xxx pure aluminum, and the other two are high-frequency welded pipes and extruded pipes of AA3003. The three kinds of composite flat tubes are composite flat tubes with AA3003, FA7805 and FA7872 as core materials. Because of the advantage in strength, the composite pipe material, especially the long-life material FA7872 as a radiator flat pipe, can be reduced by 20% to 40% compared with the three non-composite pipe materials. The application of this high-strength alloy satisfies the market demand for lighter products. The anti-corrosion performance of fins and flat tubes is also critical, and the effects of different combinations on the external anti-corrosion performance of full aluminum radiators can also be seen in subsequent experiments.

2. Full Aluminum radiator test and results

In order to compare and evaluate the corrosion resistance of these different flat tubes and their combinations, this paper adopts laboratory accelerated corrosion experiments: salt spray corrosion test, immersion test and OY solution corrosion test to evaluate the corrosion resistance of different flat tubes and their fins. External and internal corrosion resistance.

1. External corrosion test

(1) Use the salt spray corrosion test to test the corrosion resistance of the brazed side of the product. This is also the most widely used laboratory accelerated corrosion experiment at present, and it is also the laboratory accelerated corrosion experiment with the most research on the actual use of full aluminum car radiators for automotive heat exchange systems. The experimental samples were placed in the salt spray experimental box, and the main body plane formed an angle of 15 degrees with the vertical direction. The simulated seawater solution with pH of 2.6-3.0 was used as the experimental solution. During the experiment, the temperature in the box was 49±1 ℃ constant temperature. The solution spraying for half an hour and the stay for one and a half hours were alternately performed, and the relative humidity in the box was ≥98%. During the exposure experiment, the samples were regularly taken out for leak detection to determine the failure situation.

The service life of the three kinds of non-composite pure aluminum and flat tube radiators does not exceed two days, and the composite flat tube, especially the long-life material composite flat tube combination, has a service life of more than 40 days in the salt spray test. The corrosion resistance of the flat tube material is critical. At the same time, the protective effect of the fins on the flat tubes during the corrosion experiment can further prolong the service life of the radiator.

(2) Immersion experiment: After the brazing side surface of the flat tube is etched with caustic soda solution to remove part of the composite layer, it is immersed in the corrosive solution. Take out after 5 hours, treat the surface of the sample with concentrated nitric acid, clean and observe the surface morphology and cross-sectional micro-morphology. Longitudinal deep pitting corrosion occurred in pure aluminum and non-composite and composite flat tubes, while the two long-life composite tube materials only showed transverse corrosion in the surface range. This is because the diffusion precipitation zone formed between the brazing layer and the core material plays a good protective role when the long-life material is brazed.

2. Internal corrosion test

OY aqueous solution cycle experiment. The salt solution containing Cu2, Fe, Cl-, SO42- plasma and pH=3 is circulated at a constant speed inside the flat tube, and the temperature of the reaction system is regularly switched between the high temperature of 88°C and the room temperature. During the experiment, the corrosion morphology of each sample was observed regularly, and leak detection was carried out. The composite flat tube has a water-contacting side of the alloy, and the composite layer on the water-contacting side contains a certain zinc alloy element and has a lower electrode potential than the core material, thereby providing protection for the core material. The three composite flat tubes did not experience perforation failure in the 24-day cycle test.

In laboratory accelerated corrosion experiments, the poor performance of pure aluminum and non-composite materials on the brazed and wetted sides resulted in premature perforation failure of components in laboratory accelerated corrosion experiments. In actual use, it will easily fail due to corrosion and perforation, so that a one-year life cannot be guaranteed. Comparable materials should not be used as flat tubes in radiators. High-strength and long-life composite materials as automatic radiator flat tubes show excellent corrosion resistance, and provide the possibility for further thinning of materials and continuous reduction of product costs. At the same time, the proper fin collocation gives the flat tube corrosion protection and further prolongs the service life of the all aluminum radiator.

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