Study On Preparation And Properties Of Al-RE Based Amorphous Alloys

Amorphous aluminium alloys have high specific strength, good toughness and excellent corrosion resisting property, so they are new amorphous alloy metal material which has great potential of development. This study is based on Al-RE-TM (RE: rare earth; TM: transition metal). The thin amorphous alloys Al88Ce8TM4(TM=Ti, Cr, Mn, Fe, Co, Ni, Cu) was prepared successfully using single roller melt-spinning technique. Their glass-forming ability (GFA), thermodynamic and mechanical performance have been systematically investigated by X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), differential scanning calorimetry (DSC) and microhardness tester and the problem on the formation of XRD peaks in Al-based amorphous alloys are discussed.The crystal structures of Al-Ce-TM alloys were characterized by XRD and TEM. It was found that there was no sharp bragg diffraction peak but only broad dispersion peaks in the XRD pattern; There was no grain in the photographs which were taken by SEM or TEM; and selected area electron diffraction presented halo ring, so it was sure that Al-Ce-TM alloy was entirely amorphous.Thermodynamic behavior of Al-Ce-TM alloys were analyzed by DSC, and thermodynamics parameters such as amorphous crystallization activation energy, theoretical melt viscosity and brittleness of Al-Ce-TM alloy was calculated. The amorphous forming ability and thermal stability of Al-Ce-ETM alloys were formed by added early transition metal(ETM=Ti，Cr，Mn) during the cooling process of alloys’ melt were poor, amorphous forming ability and thermal stability of Al-Ce-LTM alloys which were formed by added later transition metal（LTM=Ti，Cr，Mn）during the cooling process of alloys’ melt were increased remarkably. This should be attribute to the difference in electronegativity between Al and TM: the electronegativity of Al is closed to ETM, the binding force of Al-ETM cluster is weak, the constraint effect of ETM on Al is weak, So Al is still active, the diffusion velocity was high and it crystallize easily, it shows poor amorphous forming ability and thermal stability; on the contrary, the electronegativity difference between Al and LTM is obvious, the constraint effect of LTM on Al is strong, In the condition of quenching there was no active diffusion, amorphous structure which was short-range order and long-range disorder was formed, present good amorphous forming ability and thermal stability.The hardness of amorphous sample was tested by microhardness tester. It was found that the microhardness value of strip-section was higher than roll surface because of roll surface not absorbing the pressure stress completely. Comparing the section microhardness which can represent the real hardness of strip sample, all the value of7groups was higher than HV186, and the highest value of Al88Ce8Mn4was HV247.7.Amorphous aluminium alloys which were aging in air were characterized by XRD. There was no obvious peaks in the XRD pattern, it illustrated that the alloy had good stability. But there was skin needling peaks in the XRD pattern. These peaks should be attributed to the microcrystalline grown from Al-Al cluster, Al-RE cluster and Al-TM cluster.The peaks in the XRD pattern from low diffraction angle to high diffraction angle represented Al-RE cluster, Al-TM cluster and Al-Al cluster, respectively.