Low Cycle Fatigue of Extruded and Cast Aluminium Alloy 6082

Abstract

The objective of the research is to determine the differences between the low cycle fatigue properties of an extruded and cast treatments of AA6082-T6 used as the forging billet in the production of a car suspension arm. The four treatments of the AA6082-T6 investigated are cast rod; extruded rod; cast forged; and extruded forged. Specimens are sectioned out from rods and from the forged blocks corresponding to the four treatments. All specimens are solution heat treated and aged to peak hardness. Low cycle fatigue tests are performed at total strain amplitudes between 0.37% and 0.98% and run until complete fracture. These tests were all conducted in total strain control with a strain ratio of -1. The fracture surfaces are studied using a Scanning Electron Microscope. The low cycle fatigue properties of the extruded forged AA6082-T6 seem to be better than that of the cast forged AA6082-T6 as the fatigue ductility of the cast forged were higher than that of extruded forged leading to a longer lifetime. This is concluded based on the Coffin-Manson equation, where the parameters are measures of the fatigue ductility. The ER and EF specimens has a higher yield strength and thus the cyclic stress amplitudes are higher, while the cast material has a low yield strength and the cyclic stress amplitudes are lower. The hysteresis curves of the CR and CF are wider than that of the EF and ER specimens. The cast material had a rougher fracture surface than the extruded.