Dispersoid-strengthened aluminum alloys for high temperature applications by microalloying transition elements of Zr, V, Cr, Mo and Sc

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The demand for aluminum alloys working at high temperatures (250 - 350 oC) has been greatly increased in recent years, driven by the automotive and aerospace industries requiring high strength, low cost and light components. The design of sub-micro and nano scale dispersoids in aluminum matrix is a powerful avenue to improve the strength and creep resistance at high temperatures. From our preliminary work at UQAC, it is seen that some transition elements can form either binary dispersoids (Al3M-type) during solidification and heat treatment or form more complex ternary or quaternary dispersoids in the presence of Mn, Si and Fe alloying elements, which often are thermodynamically and kinetically stable at temperatures well in excess of 300 oC. Among others, the individual and combined additions of microalloying transition elements of Zr, V, Cr, Mo and Sc are especially attractive due to high elastic modulus, high melting points, low diffusivity and relatively low cost. It is intended to select two model alloys - a wrought alloy (in 3xxx series) for deformed aluminum products and a foundry alloy (Al-Si-Mg-type) for castings - for developing dispersoid-strengthened aluminum alloys with high-temperature stability and high strength. The thermodynamic computation using the Thermo-Calc software will be first conducted to predict the phase formation and microstructure during solidification and heat treatment. The microstructures of two alloys at as-cast and heat-treated conditions with microalloying elements will be analyzed using thermal Analysis (TA), differential scanning calorimetry (DSC), optical microscopy, scanning electron and transmission electron microscopes (SEM and TEM). The dispersoid strengthening effect by individual and combined additions of Zr, V, Cr, Mo and Sc will be characterized in term of mechanical properties and creep resistance at the temperature range of 250 - 350 oC. The long term thermal stability of dispersoid-strengthened alloys will be evaluated after 1000 - 2000 h annealing at 300 oC.