Processing effects in aluminum micro-channel tube for brazed R744 heat exchangers

The effects of processing on the mechanical behavior of aluminum alloy micro-channel tubing used in brazed automotive heat exchangers are evaluated in light of the stringent requirements of CO2 (R744 refrigerant) based systems. An apparatus was developed to simulate system operating conditions of pressure and elevated temperature in tube samples. Commercially extruded and processed AA3102 micro-channel tube samples were given a simulated brazing thermal cycle and a series of static and cyclic pressure tests were performed at various temperatures. Failure stress in the tube walls was estimated and compared to tensile test data. At room temperature, the strength of the post-braze micro-channel decreased by about 17%, and about 22% at 180 °C (compared to tube that was not given a simulated brazing thermal cycle). This decrease in strength is attributed to large grains that form during the brazing thermal cycle.