Analysis of the Microstructure and Selected Properties of the Aluminium Alloys Used in Automotive Air-Conditioning Systems

The results of microstructure examinations and studies of selected mechanical properties of four aluminium alloys used in the production of automotive air-conditioning ducts (AA3103, AA5049, AA6060, AA6063) before and after the ASTM G85: A3 SWAAT Test (SeaWater Acetic Acid Test) for corrosion resistance are presented. Materials used for the manufacture of such components should be temperature stable, and therefore thermal resistance tests were carried out in a wide range of temperatures, i.e., 25 degrees C, 25 degrees C, 40 degrees C, 60 degrees C, 80 degrees C, 100 degrees C, 140 degrees C, 180 degrees C, and 220 degrees C. Annealing was performed for 72 h and 240 h, followed by cooling in water. The obtained results have proved that the non-precipitation-hardenable AA3103 and AA5049 alloys remain stable in the entire range of the investigated temperatures. The measured microhardness of these alloys was 43-46 HV0.1 for AA3103 and 56-64 HV0.1 for AA5049. The microhardness of the 6xxx series aluminium alloys was not stable in the investigated range of temperatures. The maximum was observed in the temperature range of 100-140 degrees C, which corresponded to the precipitation process of intermetallic phases, as further confirmed by microstructure observations. After the corrosion test, the mechanical properties and elongation decreased by about 5-20%.