Microstructure evolution and performances of Al-0.7Mg-0.6Si-0.2Ce-X (X=Sc, Y and Zr) alloys with high strength and high electrical conductivity

Abstract In order to achieve the compatibility between excellent mechanical properties and good electrical conductivity of Al-Mg-Si alloys, detailed investigation was carried out to understand the microstructure evolution and their influences on performances of different Al-0.7Mg-0.6Si-0.2Ce-X (X=Sc, Y and Zr) alloys prepared by casting, homogenization, hot extrusion, solution and aging treatments. Under aging state, Ce can form a large number of micron-sized AlCeSi and a few AlCeFeSi phase. The strength increased to 334 MPa as a result of decreased grain size and improved precipitation effect and the electrical conductivity increased up to 53.53%IACS because of lower solute Si atoms. The β’’ precipitates were coarsened and consequently the volume fracture was largely reduced due to the presence of Sc element, leading to the decreased strength of 311 MPa. The more solute Mg, Si and Sc atoms increased the degree of free electron scattering and the electrical conductivity decreased to 51.86%IACS. It is also found that Sc significantly enhanced the elongation of the alloy from 11.8% to 18.0%, which might be attributed to the formation of Al3Sc and (Al, Si)3Sc phases. The addition of Y raised the electrical conductivity of Al-Mg-Si-Ce alloy to 55.79%IACS by ameliorating the volume fraction and distribution of β’’ precipitates and decreasing the solute Si atoms. The co-addition of Sc and Y inherited the advantages of such two alloys. The ultimate tensile strength, elongation, electrical conductivity of Al-0.7Mg-0.6Si-0.2Ce-0.2Sc-0.1Y alloy processed by aging treatments is 336 MPa, 19.4% and 53.11%IACS, respectively.