The Effects Of Heat Treatment And Deformation On The Microstructure And Properties Of Light Weight & High Strength Aluminium Alloys With Sc Element

Rare earth scandium(Sc) has been considered as the most efficient modificator in the alloys due to its function in grain refinement, recrystallization resistance and dispersion strengthening. As the new generation of ultra high strength structural materials, Al-Zn-Mg-Cu-Sc-Zr alloy has attracted much attention. However, the application of Al-Zn-Mg-Cu-Sc-Zr alloy is limited because of its high cost and that it can hardly possess both high strength and elongation. Therefore, it is necessary to optimize the heat treatment and deformation process to improve the comprehensive performance and deduce the cost of Al-Zn-Mg-Cu-Sc-Zr alloy.Ultra high strength Al-Zn-Mg-Cu-Sc-Zr alloys were prepared, and the effects of homogenization treatment(temperature, duration and cooling way), hot-extrusion(temperature and extrusion ratio) and aging process on the microstructure and properties of the alloys were studied. Furthermore, the strengthening mechanism of Al-Zn-Mg-Cu-Sc-Zr alloys was investigated and analyzed. The main conclusions are listed as follows:Both the non-equilibrium phases(MgZn2) and elements segregation in the as-cast alloy could be eliminated after homogenized at 470°C for 1 h followed by water cooling, fitting well with the results of homogenization kinetics equation.The grains could be obviously refined by hot-extrusion, improving the mechanical properties of alloys. A new process(homogenization at 470°C for 1 h followed by hot-extrusion immediately) was introduced to reduce energy consumption and condense the period of process without degradation of mechanical properties of alloys.The parameters of aging procedure(aging temperature and duration) have important impacts on the microstructure and mechanical performance of Al-Zn-Mg-Cu-Sc-Zr alloys. As the aging temperature raised, the alloys could reach the stage of peak aging with higher hardness and less time. The formation of GP zones and ?' phase during the aging process could significantly enhance the mechanical properties of alloys, especially the yield ratio. The alloy aged at 120°C exhibited a dual-peak hardening trend, which was likely attributable to the overlap between the formation of GP zones and the precipitation of ?' phase. Excellent mechanical properties could be obtained after solution-aging treatment: ultimate tensile strength was 746.9 MPa, yield strength was 724.2 MPa and the elongation was 10.9%. The increase in yield strength is attributed to the synergistic effect of addition of Sc and Zr, hot-extrusion and solution-aging process. The addition of Sc and Zr could cause a 14% increase in yield strength.