Aluminum Alloy Based Nanocomposites Strengthened with Amorphous AlNiTiZr Phase

Abstract

The concept to design a composite of the 7475 alloy strengthened with particles of an amorphous aluminum based alloy was studied in the present paper. Mechanical alloying (MA) process was applied to obtain amorphous structure of the powder of composition Al70Ni10Zr10Ti10 (in at%). Elemental powders of this composition were ball milled for 60 h in a planetary high energy mill using steel balls. The estimated mean size of powder particles below 10 μm was much smaller than that of the initial elemental powders. The mean value of the microhardness of the milled powder was 384 HV and was significantly higher than that of initial powders. The dominant presence of the amorphous structure was confirmed using DSC studies, in which crystallization peaks were observed above 400°C. X-ray diffraction (XRD) patterns after various milling times confirmed a partial amorphization of the material. Additionally, weak maxima of Al3Zr4 phase were identified. TEM studies of powders confirmed the formation of predominantly amorphous structure with some nanocrystalline inclusions of intermetallic phases identified as Al3Zr4, AlZr3, Al3Ni and Al3Ti. The amorphous powder was mixed (for a short time) with prealloyed 7475 alloy powder 40 h ball milled to obtain nanocrystalline grain size of powder’s particles. Powders were hot pressed in vacuum, below the crystallization temperature at 380°C and pressure of 600 MPa in order to preserve amorphous and nanocrystalline grain structure. SEM studies of the composite containing 1/3 ball milled 7475 alloy and 2/3 of the amorphous powder allowed identifying low porosity and clean interface within the composite. The samples showed compression strength near 500 MPa and a few percent ductility. The cracks nucleated within the amorphous particles as resulted from SEM studies of the compressed samples.