Synopsis
Aluminum casting alloys, post-solidification cooling conditions play a critical role in determining the final mechanical properties. Quench delay time refers to the interval between solution treatment and
rapid cooling prior to aging, and it has a significant effect on the mechanical properties of precipitation- heat-treatable aluminum alloys. In cast alloys, quench delay can influence diffusion and precipitation behavior, delaying the nucleation of precipitates during aging and consequently leading to a reduction in strength. In addition, this effect should be evaluated together with dendrite arm spacing, and materials with finer microstructures are reported to be more sensitive to such delays. Quench delay also allows natural aging to occur before artificial aging; the secondary phases formed during this process may reduce precipitate nucleation and thereby decrease precipitation efficiency. Therefore, controlling quench delay is of great importance for achieving high strength and hardness in Al–Si–Mg alloys widely used in automotive and structural applications.
In this study, the effect of post-casting quench delay on the microstructure and mechanical properties of AlSi9Mg alloy was experimentally investigated. Samples produced under the same casting conditions were held for 45, 90, 120, 150, and 180 seconds before quenching, followed by T5 temper treatment. Microstructural examinations were carried out using optical microscopy, and secondary dendrite arm spacing (SDAS) was measured. Mechanical properties were determined by hardness and tensile tests.
The results showed that increasing delay time led to noticeable microstructural coarsening and a reduction in mechanical properties. The SDAS value of the sample quenched after 180 seconds increased by approximately 34% compared to the sample quenched after 45 seconds. In contrast, the post-heat-treatment hardness decreased by about 7%. Considering the average tensile test results, the average tensile strength decreased by 10%, while the average yield strength decreased by approximately 7%. These results clearly reveal an inverse relationship between the increase in dendrite arm spacing and the decrease in mechanical properties with increasing delay time. The findings indicate that rapid cooling improves mechanical properties, whereas quench delay causes a deterioration in these properties.
In conclusion, this study demonstrated the effect of quench delay on the microstructure and mechanical properties of AlSi9Mg alloy. The findings showed a clear relationship between increasing delay time, increasing SDAS, and decreasing mechanical properties. In this respect, the study contributes to a better understanding of the effect of post-casting cooling conditions on the final properties of the material.
