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<p>This study investigates the detailed comparison of the microstructure, mechanical properties, fatigue crack growth behaviour, and fracture toughness of a stir-cast Al-Cu alloy under T6, T8, and T9 temper conditions. The T9 temper condition exhibits the highest ultimate strength (<i>σ</i><sub>UTS</sub>), which increases by ~ 24% over T6 and ~ 70% over the solution-treated condition. Microstructural analysis reveals that this improvement arises from the synergistic effect of refined<i> θ</i>′ precipitates, high dislocation density, and deformation-induced structures, including dislocation cells and deformation bands. In comparison with T6, the T8 temper condition shows moderate strengthening primarily due to precipitation and grain refinement. The T9 temper condition demonstrates superior fatigue resistance with a steeper Paris regime and a higher stress intensity factor (ΔK ~ 34&#xa0;MPa√m) compared to T8 (~ 31&#xa0;MPa√m) and T6 (~ 24&#xa0;MPa√m) conditions. The conditional fracture toughness (J<sub>Q</sub>) also increases significantly in the T9 condition. These improvements are attributed to enhanced crack-tip shielding mechanisms, including crack deflection and plastic zone heterogeneity induced by dislocations-precipitates interactions. Overall, the results show that the T9 temper condition provides high strength, fatigue resistance, and fracture toughness through the combined effects of grain boundary, precipitation, and dislocation strengthening mechanisms.</p>

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The Effect of Heat Treatments on Fatigue Crack Growth Rate and Fracture Toughness of Al-Cu Alloy

  • 期刊论文

  • 发表日期：

    2026年7月22日

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  • Vishal Gupta,
  • Pallavi Singh,
  • Nikhil Kumar

摘要

This study investigates the detailed comparison of the microstructure, mechanical properties, fatigue crack growth behaviour, and fracture toughness of a stir-cast Al-Cu alloy under T6, T8, and T9 temper conditions. The T9 temper condition exhibits the highest ultimate strength (σUTS), which increases by ~ 24% over T6 and ~ 70% over the solution-treated condition. Microstructural analysis reveals that this improvement arises from the synergistic effect of refined θ′ precipitates, high dislocation density, and deformation-induced structures, including dislocation cells and deformation bands. In comparison with T6, the T8 temper condition shows moderate strengthening primarily due to precipitation and grain refinement. The T9 temper condition demonstrates superior fatigue resistance with a steeper Paris regime and a higher stress intensity factor (ΔK ~ 34 MPa√m) compared to T8 (~ 31 MPa√m) and T6 (~ 24 MPa√m) conditions. The conditional fracture toughness (JQ) also increases significantly in the T9 condition. These improvements are attributed to enhanced crack-tip shielding mechanisms, including crack deflection and plastic zone heterogeneity induced by dislocations-precipitates interactions. Overall, the results show that the T9 temper condition provides high strength, fatigue resistance, and fracture toughness through the combined effects of grain boundary, precipitation, and dislocation strengthening mechanisms.