Fatigue Behavior Of Extruded Al-Mg-Si-(RE) Alloys

With a wide application of Al-Mg-Si alloy 6063 with good integrative performances in aeronautic and astronautic,automotive as well as architectural industries,the higher mechanical properties are required for the alloy.For various structural materials,fatigue is one of its main failure forms.For those aluminum alloys,the same case is also true. Obviously,the investigation concerning fatigue behavior of Al-Mg-Si-(RE) alloys is of both academic and practical significance.In order to provide a reliable theoretical foundation for both fatigue resistant design and reasonable usage of these aluminum alloys, both fatigue deformation and fracture behaviors of the extruded 6063 and 6063-0.5%Ce alloys with different processing states has been investigated,and the influence of Ce and heat treatment on the fatigue behavior of the extruded 6063 and 6063-0.5%Ce alloys are determined.The experimental results show that the extruded 6063 and 6063-0.5%Ce alloys subjected to different processing and treatment exhibit cyclic hardening,softening and stability,which depends on the composition,heat treatment and imposed total strain amplitude.For the extruded 6063 alloys with as-extruded and solution treated states,the addition of Ce can effectively enhance both cyclic deformation resistance and fatigue life of the alloys.For the extruded 6063 alloys with solution plus aging treated states,the addition of Ce decrease its cyclic deformation resistance while has no significant influence on the fatigue life of the alloy.The solution plus aging treatment can increase the cyclic deformation resistance of the extruded 6063 alloy,but decrease the cyclic deformation resistance of the extruded 6063-0.5%Ce alloy.However,the solution treatment leads to a decrease in the cyclic deformation resistance of both extruded 6063 and 6063-0.5%Ce alloys.In addition,the solution plus aging treatment can effectively improve the fatigue lives of the extruded 6063 and 6063-0.5%Ce alloys.For as-extruded 6063 and 6063-0.5%Ce alloys,a single-slope linear relation between elastic strain amplitude,plastic strain amplitude and reversals to failure is observed.For the extruded 6063 and 6063-0.5%Ce alloys subjected to both solution and solution plus aging treatments,the single-slope linear relation between elastic strain amplitude and reversals to failure is noted while a two-slope linear relation between plastic strain amplitude and reversals to failure is observed.The observations on fracture surface of fatigued specimens reveal that under the condition of fatigue loading controlled by total strain amplitude,the fatigue cracks initiate in a transgranular mode at the surface of fatigue specimens,and propagate transgranularly for the extruded 6063 and 6063-0.5%Ce alloys with different processing states.