Improvement of microstructure and mechanical properties of Al-Cu-Li-Mg-Zn alloys through water-cooling centrifugal casting technique

Abstract

The microstructure and mechanical properties of as-cast Al-Cu-Li-Mg-Zn alloys fabricated by conventional gravity casting and centrifugal casting techniques combined with rapid solidification were investigated. Experimental results demonstrated that compared with the gravity casting technique, the water-cooling centrifugal casting technique significantly reduces porosity, refines α(Al) grains and secondary phases, modifies the morphology of secondary phases, and mitigates both macro- and micro-segregation. These improvements arise from the synergistic effects of the vigorous backflow, centrifugal field, vibration and rapid solidification. Porosity and coarse plate-like Al₁₃Fe₄/Al₇Cu₂Fe phase result in the fracture before the gravity-cast alloy reaches the yield point. The centrifugal-cast alloy, however, exhibits an ultra-high yield strength of 292.0 MPa and a moderate elongation of 6.1%. This high yield strength is attributed to solid solution strengthening (SSS) of 225.3 MPa, and grain boundary strengthening (GBS) of 35.7 MPa. Li contributes the most to SSS with a scaling factor of 7.9 MPa·wt.%^-1. The elongation of the centrifugal-cast alloy can be effectively enhanced by reducing the porosity and segregation behavior, refining the microstructure and changing the morphology of secondary phases.