摘要 :
Nanostructured Al-Zn-Mg-Cu alloy and boron carbide/Al-Zn-Mg-Cu composite powders are fabricated through cryomilling. eta'-MgZn2 precipitation in each material is characterized through differential scanning calorimetry. The activat...
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Nanostructured Al-Zn-Mg-Cu alloy and boron carbide/Al-Zn-Mg-Cu composite powders are fabricated through cryomilling. eta'-MgZn2 precipitation in each material is characterized through differential scanning calorimetry. The activation energy of eta' precipitation is derived through Kissinger analysis. The addition of boron carbide to nanostructured Al-Zn-Mg-Cu powder increases the onset and peak temperatures of ' precipitation, but do not significantly affect the activation energy. Further analysis of uncertainties in measurement indicates that weighted least squares linear regression is a more reliable method that supplements the use of differential scanning calorimetry as a method for rapid characterization of precipitation in materials.
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摘要 :
Thermal stability of Al-Si alloys and their composites is an important property for their application in engine components. In this work the thermal expansion and the physical Coefficient of Thermal Expansion (CTE) of AlSi1.1, -1....
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Thermal stability of Al-Si alloys and their composites is an important property for their application in engine components. In this work the thermal expansion and the physical Coefficient of Thermal Expansion (CTE) of AlSi1.1, -1.7, -7, -12 alloys and AlSi7/Al_2O_3/20s short fibre composite material are presented. The higher the Si content the more decreases the expansion of the alloys. Random planar alumina fibres reduce the in-plane thermal expansion, but the transverse expansion is significantly increased with respect to the matrix. The precipitation kinetics of Si is studied by means of Differential Scanning Calorimetry (DSC). Precipitation peaks correlate with an increase in the CTE of the alloys and the composite. Al-Si alloys with 7 wt. percent and higher content of Si present a percolating Si-network in the as-cast condition. The disintegration of this network during solutionizing results in a decrease of the hardness of the alloy. On the other hand, the hardness of the composite is increased during solution treatment via the formation of Si bridges between the short fibres, which strengthen the Si/Al_2O_3-network. The reinforcing networks' architecture is revealed by deep etching. It causes reversible viscous flow of the Al-matrix at temperatures > 300 deg C.
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