The Synthesis And Crystallization Behavior Of Amorphous Nanocrystalline Al-based Alloys With High Strength And Heat Resistant

Compared with the traditional aluminum alloy,the performance of the aluminum based amorphous alloy was improved greatly,but the heat resistance is very poor and easy to crystallize.Therefore,the research and development of new aluminum alloy materials,further improving the strength,hardness and heat resistance of aluminum alloy,can better expand the application of aluminum alloy.Multicomponent Al-based alloys with compositions of Al₈₄Y₉Ni₄Co_1.5Fe_0.5TM₁（TM is transition metal element,TM=Zr,V,Nb,Cr,Mn,Mo,Cu,Au,Ag）were chosen in this project.The amorphous nanocrystalline alloy with high hardness and heat resistance was successfully prepared.Alloy ribbons were prepared by single-roller melt-spinning,and conical alloy rods were prepared by injection copper-mold casting.This dissertation investigated the ability of amorphous formation,thermal stability,the evolutions of the structures and mechanical properties by X-ray diffractometer（XRD）,differential scanning calorimeter（DSC）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and optical microscopy（OM）etc.The main research results are as follows:（1）Multicomponent Al-based alloys of Al₈₄Y₉Ni₄Co_1.5Fe_0.5TM₁（TM=Zr,V,Nb,Cr,Mo,Mn,Fe,Co,Ni,Cu,Ag or Au）with ultrahigh hardness can be maintained at elevated temperatures were prepared in this project.（2）The crystallization process of Al₈₄Y₉Ni₄Co_1.5Fe_0.5TM₁ glassy alloys were studied systematically,and the influence of different elements addition on the glass transition of the alloys were statistically analyzed.The reverse transformation of the primary precipitates of fcc-Al and Al_xM_y in Al₈₄Y₉Ni₄Co_1.5Fe_0.5TM₁ amorphous alloy induced by heating was studied.（3）The Vickers hardness of as-spun Al₈₄Y₉Ni₄Co_1.5Fe_0.5TM₁amorphous alloys are 360～430.After being annealed at 600 K～680 K,the Al-based alloys with the structure of[fcc-Al+am″]was obtained,and the Vickers hardness of the alloys are increased to 550～580,showing high hardness and high heat resistance.The microstructure and kinetics of the alloy after heat treatment were analyzed,the results show that the Al-based amorphous nanocrystalline alloy with fcc-Al nanocrystalline phase and amorphous phase has extremely high hardness and thermal stability.（4）Conical alloy rods were prepared by injection copper-mold casting,in the conical cast rod,an amorphous single phase is formed for diameter up to about 0.82mm,while the diameter for[fcc-Al+am]phases extends to about 1.2 mm.The cast[fcc-Al+am]alloys exhibit a high Vickers hardness of about 510,which decreases rapidly to 260 in the fully crystalline phase mixture.