An investigation into the softening behavior of cast A356 alloy in the solid and semisolid deformation regimes

The current work deals with the hot deformation behavior of A356 aluminum alloy starting with the cast structure and an emphasize on the capability of flow softening. Toward this end, the hot compression tests were performed at temperatures of 150, 250, 350, 450, 500 and 550 degrees C in the solid range and 580 degrees C in the semisolid range under the typical strain rate of 0.01s- 1. The materials represent high protentional for the occurrence of softening mechanism in solid state regime. During thermomechanical processing (above 250 degrees C), after reaching the peak stress, the dynamic recrystallization prevails over the deformation behavior and the stress level reaches a steady state regime. The alpha-dendritic arms are crushed and refined, and the silicon blades are mechanically fragmented and spread irregularly through the microstructure. Being in the semi-solid temperature range, the eutectic silicon phase is melted and causes a sharp decrease in the resistance against deformation. The penetration of the liquid phase along the developed sub-boundaries give rise to grain partitioning and resembles the occurrence of dynamic recrystallization. The presence of the liquid phase during semisolid forming, in addition to the lubricated flow mechanism, facilitates the deformation by providing proper condition for the occurrence of recrystallization. In the present case, a stable stress level as below as 1 MPa was recorded for the experiment cast structure.

Automated summary

This study focuses on the hot deformation behavior of A356 aluminum alloy, particularly its flow softening capability. The results show that dynamic recrystallization dominates the deformation behavior at temperatures above 250°C, leading to a steady state stress level. In the semi-solid temperature range, the melting of eutectic silicon phase causes a sharp decrease in resistance against deformation, and the penetration of liquid phase along sub-boundaries results in grain partitioning, resembling the occurrence of dynamic recrystallization.