Ageing of Brazed Aluminium AA6xxx Alloys for Vehicle Radiators

Abstract:

Some aluminium alloys with Mg-Si age-hardening are used in vehicle radiators. For cost reasons they are preferably delivered in a naturally aged temper. Estimated minimum time of natural ageing between brazing and when the radiator is taken into service is 14 days. At the service temperature of 95°C, the radiator material will continue to age harden. For accelerated durability testing it is vital to use a radiator with the strength and ageing response of a service radiator. We investigated whether the full 14 days of natural ageing were needed, or if the time could be shortened. Since a vehicle is not in constant use, the radiator temperature will vary over time. We therefore compared cyclic ageing between ambient temperature and 95°C to continuous ageing at 95°C. The Sapa Heat Transfer alloys FA7870 (for headers) and FA7850 (for tubes) were subjected to different ageing times at different temperatures. Tensile and hardness were performed to assess the ageing effect. It was found that natural ageing reduced hardening during the subsequent ageing at service temperature ageing effect, an effect that was most pronounced for the first four days. There was no difference between continuous and cyclic ageing.

• Periodical: Materials Science Forum (Volumes 794-796)
• Pages: 1239-1244
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.794-796.1239
• Online since: June 2014
• Authors: Torkel Stenqvist*, Kristoffer Bång, Sören Kahl, Arnaud Contet, Oskar Karlsson
• Keywords: Al-Mg-Si Alloy, Braze Clad Alloys, Brazing, Heat Exchanger, Low Temperature Ageing, Natural Aging, Pre-Aging, Radiators

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