Abstract:The effects of Si addition and applied pressure on the microstructure and tensile properties of as-cast Al-5.0Cu-0.6Mn- 1.2Fe alloys were studied. The results show that Si addition promotes the formation of Chinese script α-Fe, and suppresses the precipitation of Al₃(FeMn) and Al₆(FeMn). For the alloys produced without pressure, Si addition increases the volume fraction of porosity, resulting in remarkable decrease in ultimate tensile strength (UTS) and yield strength (YS). For the alloys produced with 75 MPa pressure, Si addition improves UTS and YS owing to the formation of high number density of Al₂Cu (θ) phases. The tensile properties of alloys increase with increasing applied pressure at the same Si content level, which is attributed to elimination of porosity, grain refinement strengthening and solid-solution strengthening. The alloy with 1.1% Si addition and 75 MPa pressure shows the best tensile properties, where the UTS, YS and elongation are 237 MPa, 140 MPa and 9.8%, respectively.

Key words: Al-Cu alloys; Si addition; solidification; tensile properties; microstructure