Abstract
Abstract Since automotive heat exchangers are operated at varying temperatures and under varying pressures, both static and dynamic mechanical properties should be known at different temperatures. Tubes are the most critical part of the most heat exchangers made from aluminum brazing sheet. We present tensile test, stress amplitude-fatigue life, and creep–rupture data of six AA3XXX series tube alloys after simulated brazing for temperatures ranging from 293 K to 573 K (20 °C to 300 °C). While correlations between several mechanical properties are strong, ranking of alloys according to one property cannot be safely deduced from the known ranking according to another property. The relative reduction in creep strength with increasing temperature is very similar for all six alloys, but the general trends are also strong with respect to tensile and fatigue properties; an exception is one alloy that exhibits strong Mg-Si precipitation activity during fatigue testing at elevated temperatures. Interrupted fatigue tests indicated that the crack growth time is negligible compared to the crack initiation time. Fatigue lifetimes are reduced by creep processes for temperatures above approximately 423 K (150 °C). When mechanical properties were measured at several temperatures, interpolation to other temperatures within the same temperature range was possible in most cases, using simple and well-established equations.
Highlights
MOST automotive heat exchangers are today made from aluminum sheet
It is often more challenging to fulfill the requirements on mechanical durability than the functional requirements on heat transfer. This is especially true for applications such as charge air coolers for heavy vehicles, but the durability requirements for other types of automotive heat exchangers have become more demanding
We have investigated tensile test, fatigue, and creep properties of five non-heat-treatable and one heattreatable AA3XXX-series heat exchanger tube alloys for temperatures ranging from room temperature to 573 K (300 °C)
Summary
Operating pressures and temperatures have been increasing while material thicknesses have been decreasing. This is a continuous development motivated by the task to reduce vehicle weight and toxic emissions and to improve fuel efficiency. It is often more challenging to fulfill the requirements on mechanical durability than the functional requirements on heat transfer. This is especially true for applications such as charge air coolers for heavy vehicles, but the durability requirements for other types of automotive heat exchangers have become more demanding.
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