Investigating Porosity Tolerance and its Impact on the Deformation Behavior of HPDC Al-8Si-0.5Mn-0.5Mg-0.2Cu-3Zn Alloys
摘要
Optimizing the strength-ductility synergy in HPDC alloys via heat treatment requires carefully managing the trade-off between beneficial microstructural evolution and detrimental gas porosity expansion. In this study, HPDC Al-8Si-0.5Mn-0.5Mg-0.2Cu-3Zn alloys were T6 solution treated at 490°C and 530°C for different times (20 min, 40 min, 60 min) followed by water quench and immediate artificial aging at 180°C for 60 minutes. The resulting microstructure characteristics and deformation behavior were systematically investigated. The results revealed that the porosity volume and elongation at as-cast state are 0.36% and 5.3%. As the solution time increased from 20 min to 60 min at 490 °C condition, the porosity volumes were 0.369%, 0.500% and 0.450%. The related values of elongation were 17.2%, 16.5%, and 19.3%, respectively. The morphology and volume of both gas porosity and shrinkage porosity showed negligible change at 490 °C condition. The gas porosity was seriously expanded at 530 °C condition, the observed porosity volumes are 1.02%, 3.74%, and 6.13%, and the related elongation are 15.2%, 17.7%, and 0.54%. The increasement of ductility at 490 °C and 530 °C condition was mainly contributed by the dissolution of secondary phase and the spheroidization of eutectic. The yield strength and ultimate strength at 530 °C are significantly higher than at 490 °C condition. Compared with the elongation at 490 °C for 40 min, the elongation at 530 °C for 40 min is comparable even seven times porosity volume increasement. The gas porosity with suitable volume and critical diameter has not detrimental to the ductility of HPDC alloys, and the tolerance of the critical diameter value for the expanded gas porosity, under the present experimental conditions, is smaller than 100 μm, provided the pores are highly spherical.