Effect of Overaging on the Cyclic Deformation Behavior of an AA6061 Aluminum Alloy

Abstract

The present work encompasses the effect of overaging on the strain-controlled low-cycle fatigue (LCF) behavior of an extruded AA6061 aluminum alloy at varying strain amplitudes. During the T7 aging treatment, the size of precipitates increased from 60 nm under T6 conditions to 220 nm after aging for 48 h at 200 • C, leading to a decrease in the monotonic tensile strength. During the LCF tests, nearly symmetrical hysteresis loops can be observed in the mid-life cycle under all test conditions, whereas the first-cycle hysteresis loops were moderately inflected under long-aging conditions. With increasing aging time, the cyclic peak stresses decreased and the plastic strain increased. Nearly ideal Masing behavior was exhibited under T6 conditions, while it was lost under T7 overaging conditions. The cyclic stress responses were similar under all tested conditions, involving stabilization at low strain amplitudes and softening at high strain amplitudes, with initial hardening for the first few cycles. Compared to the T6 condition, the fatigue life increased with increasing T7 aging time. Various LCF parameters were estimated based on the Coffin-Manson and Basquin relationships and on the LCF experimental results. The relationship between the fatigue life, strength, and microstructure of the investigated AA6061 aluminum alloy under various aging conditions was discussed.

Thermo-Mechanical Fatigue Behavior and Resultant Microstructure Evolution in Al-Si 319 and 356 Cast Alloys

“…Additionally, striations were observed in both the 319 ( Figure 6 c) and 356 ( Figure 6 e) alloys. The interspacing of the striations in the 356 alloy was larger than that in the 319 alloy, indicating faster fatigue propagation during TMF cycling [ 27 ].…”

On the low-cycle fatigue behavior of thermo-mechanically processed high-strength aluminum alloys

“…In case of significant contribution of plastic strain, half-life hysteresis loops of both alloys remain relatively symmetrical. Since slip during cyclic plastic straining is the dominant deformation mechanism in face-centered cubic (fcc) metals, symmetrical loops are often seen during LCF testing [39,52]. The areas of hysteresis loops are an indication of the relevant energy dissipation per cycle [60][61].…”

“…In another study, aging of AA6063 alloy at temperatures between 160 °C and 200 °C for 7 to 9 h led to an opti-mal fatigue performance [30]. It was also shown that fine precipitates can improve the properties of AA6061 and AA2024 alloys under cyclic loading [34,39]. However, the growth of the formed precipitates imposed by a higher aging temperature adversely affected the fatigue behavior of these alloys.…”

“…Furthermore, the impact of various heat treatments and related precipitation processes on the cyclic behavior of aluminum alloys was analyzed [29][30]34,39]. In one of these studies the effect of different aging conditions on the high-cyclic fatigue (HCF) behavior of AA7075 alloy was explored [29].…”

Effect of Al 6061 Alloy Compositions on Mechanical Properties of the Automotive Steering Knuckle Made by Novel Casting Process

“…To improve the mechanical properties of steering knuckles, we evaluate various compositions of Al alloys by analyzing their thermal properties, such as thermal stress, shrinkage starting temperature (SST), shrinkage characteristics, and pore formation. In addition, like previous studies, we perform forging and heat treatment to further improve the mechanical strength of the steering knuckles [13]. surface of the molten metal.…”