Ageing characteristics and high-temperature tensile properties of Al-Si-Cu-Mg alloys with micro-additions of Cr, Ti, V and Zr

Ageing characteristics and high temperature tensile properties of the Al-7Si-1Cu-0.5Mg (wt%) alloy modified with transition metals Cr, Ti, V and Zr, were tested. The modified alloy formed the Cr/Ti/V/Zr-rich dispersoid phases with a variety of morphologies. During isochronal ageing, the alloy reached a peak hardness of 92 HRF after a cycle at 200 °C for 1 h. The tensile test at room temperature showed that alloying additions increased the yield stress by 30% and ultimate tensile strength by 5%. With increasing the testing temperature from 25 °C to 300 °C, the yield strength and tensile strength decreased from 300 MPa to 184 MPa and from 313 MPa to 196 MPa, respectively. Fractographic analysis after tensile testing revealed that coarse intermetallics influenced the crack propagation. At lower temperature, the cleavage-type brittle fracture was dominant while at higher temperature the fully ductile cracking mode was present. It is believed that the Cr, Zr, Ti and V-containing dispersoid phases improved the alloy strength at the elevated temperature.