Increased hot forgeability of 2024Al/Al₁₈B₄O₃₃w whisker composites at high strain rates

Whisker reinforced aluminum alloy composites are attractive for structural applications in automotive and aerospace applications. However, their forgeability is limited by their poor ductility at room temperature. The effects of temperatures (350–520 °C) and strain rates (0.01–50 s⁻¹) on the resistance to microcracking and on the closure of voids are investigated for 2024Al/Al₁₈B₄O₃₃w whisker composite as well as unreinforced AA2024 alloy. Under elevated temperature and high strain rate (>450 °C, >1.0 s⁻¹), there are less cracks and no axial splitting on the surface of 2024Al/Al₁₈B₄O₃₃w composite. Test results show lower flow stresses and incipient melting at higher temperatures enable better tolerance of whisker-matrix strain mismatch at the interface during hot compression resulting in increased stabilization of flow stresses. While higher strain rates contribute to increased strain rate hardening, whisker rotation and void closure. It is interesting to note that the unreinforced AA2024 alloy experiences flow localization, surface cracking and plastic instability at temperatures higher than 450 °C but the presence of Al₁₈B₄O₃₃ in the composite seems to better resist these failure mechanisms resulting in higher forgeability.