Abstract
In this investigation, both Scandium (Sc)-added and Sc-free Al-Zn-Mg-Cu aluminum alloys were prepared by spray forming. The as-deposited alloys were hot extruded and then subjected to solid solution and aging treatment at different temperatures. The effect of minor scandium addition on microstructure evolution and mechanical properties were studied. The results revealed that, with Sc added spray formed alloy (7055Sc alloy), Sc element was mainly observed in the primary Al3(Sc,Zr) phase, the secondary Al3(Sc,Zr) phase and the W(AlCuSc) phase in the alloy. Compared to the alloy without Sc addition (7055 alloy), the effects of fine grain strengthening, dislocation strengthening and precipitation strengthening of Al3(Sc,Zr) phase were enhanced. At low aging temperature, the precipitation of MgZn2 phase was inhibited and the size of this phase was found large in the 7055Sc alloy. Therefore, after 120 °C for 24 h aging, the yield strength of 7055Sc alloy was tested as 603.4 MPa, which was 46.9 MPa lower than that of 7055 alloy at the same aging temperature. After 160 °C for 24 h aging, in the 7055Sc alloy the quantity and density of MgZn2 phase increased and the size of the phase was smaller. As a result, the yield strength of the 7055Sc alloy was 576.9 MPa, which was 31.6 MPa higher than that of the 7055 alloy. The effects of Sc on the aging precipitation of spray formed 7055Sc alloy at different aging temperatures were explained by the vacancy mechanism of diffusion.
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