The application of medium high strength aluminium alloys in fatigue loaded automotive parts and aspects of material temper and microstructureTuesday (26.05.2020) 11:30 - 11:50
The advantage of using medium to high strength aluminium alloys like the AA6082 in fatigue loaded parts in automotive chassis are many, of importance are the strength to weight ratio and high resistance to corrosion.
On the other hand, the combination of formability and high degree of forming technological freedom in producing parts are as well key factors. Processes like casting, extrusion, rolling or forging can give high quality parts for automotive applications in strong competition with steel solutions. To utilise the material the combination of chemical composition and the thermomechanical processing (TMP) should be understood since there is a strong relation to final product performance and in inherent properties. The fatigue is as critical as any other property with respect to be influenced by microstructural features as grain size, particle structure and hardening temper.
In the area of forgings experimental work with the AA6082 strongly link the recrystallized grain size in the final product to fatigue lifetime, a reduction of cycles to failure can be reduced by a factor of 10. In case of coarse grains, the ductility also decreases, and the overall product performance drops significantly if the recrystallization behaviour not properly controls during TMP.
Another issue is the hardening temper where in many cases the maximum hardness is chosen as final state of the properties. When plastic capacity and cyclic work hardening is a part of the discussion as in low cycle fatigue regime, the max hardness is contradiction. From temper T6 to an overaged temper T7X a significantly change in plastic response occurs. Correct ageing procedure should be chosen in cases of optimised design in a low cycle fatigue situation, typical for many chassis' parts.
The automotive industry is searching for lightweight solutions to meet emission regulations. However, the material and thermomechanical process integration must have a focus on microstructural issues in the final product to reach this performance demand.