Research On The Interface Structure And Mechanical Properties Of Fe-based Amorphous Reinforced Magnesium Matrix Composites

Magnesium alloy as the "21st century green engineering materials",has a series of excellent mechanical and physical properties,is widely used in aerospace,defense industry,3C(communication,computer,consumer electronics)products and transportation and other fields.However,due to the low modulus of elasticity of magnesium and magnesium alloy,the use of magnesium is severely limited.Scholars often use a series of traditional reinforcements such as Si C,carbon fiber and carbon nanotubes,which can significantly improve the elastic modulus of Mg matrix composites,but at the cost of a significant decrease in composite plasticity,which is caused by the poor interfacial bonding between traditional reinforcements and Mg matrix.Therefore,improving the interfacial bonding of Mg-matrix composites to make the Mg-matrix composites increase the strength without decreasing the plasticity at the same time becomes a key problem that needs to be solved urgently.In this thesis,magnesium matrix composites reinforced with different mass fractions of spherical amorphous particles(99.8% magnesium powder as the matrix material)were prepared by discharge plasma sintering technique,and the microstructure of the interface was observed by scanning electron microscopy and transmission electron microscopy.The connection between "interface microstructure-mechanical properties-failure behavior" was established by the observation of fracture morphology.High-density Mg O/Mg composites were successfully prepared by the SPS process,and in the samples,the nano-Mg O particles were biased around the interface to form a distinct Mg O interfacial layer.The Mg O showed different morphologies at the interface and presented a perfect co-grid interface with the matrix.It was found by nanoindentation test that the mechanical properties at the interface were coherent and the interfacial elastic modulus was 43.7 GPa,and there were no obvious pores;it was observed by TEM that the nano Mg O at the interface could effectively hinder the movement of dislocations and form dislocation cells with a size of 720 nm at the interface,and it was also because of the plugging of dislocations at the interface and the high elastic modulus that caused the Mg O/Mg The failure of the composite is in the form of fracture along the crystal.After the addition of 50 wt.% of iron-based amorphous to pure magnesium,it was found that the amorphous was deformed to some extent during the sintering process,and the amorphous-amorphous contact interface was partially fused.And the addition of amorphous can significantly improve the thickness of the interfacial oxide layer,mainly due to the presence of some chemically active elements(Cr,Mo,B)in the amorphous,these elements adsorb the residual oxygen elements in the magnesium matrix,improve the matrix interface and reduce the thickness of the Mg O layer.In addition,the addition of amorphous can significantly sacrifice only 2.2% elongation and significantly improve the mechanical properties of Mg matrix composites,the maximum tensile strength is increased from 156 MPa to 192 MPa for pure Mg.The change of interfacial organization induces a change in the fracture mechanism of the composites,from along-crystal fracture to quasi-dissociation fracture.After adding 10 wt.%,20 wt.%,30 wt.% and 40 wt.% to pure magnesium,it was found that in the magnesium matrix composites with small amount of amorphous particles,the amorphous reinforcement was uniformly distributed and no obvious agglomeration occurred,and when the amorphous content increased to 30 wt.%,the amorphous reinforcement had a tendency to deviate towards the grain boundary.At the same time,with the increase of the amorphous particle content,the fracture mechanism of the material also undergoes an obvious change from fracture along the crystal(<30 wt.%)to quasi-dissociation fracture,and 30 wt.% amorphous content is the transition point of the fracture mechanism.Similarly,at amorphous content less than 30 wt.%,the number of dissociation steps and tearing ribs on the fracture surface is small and the strength and plasticity of the material do not change significantly.However,when the amorphous content was increased to 40 wt.%,the mechanical properties of the magnesium matrix composites were significantly increased from142.1 MPa to 156.0 MPa.In conclusion,the addition of Fe-based amorphous particles thins the Mg O layer at the interface of the Mg matrix in the Mg matrix composites,which is due to the release of alloying elements(Cr,Mo,B)from the amorphous particles into the matrix by SPS sintering,which has the effect of improving the structure of the matrix interface;due to the thinning of the oxide layer at the interface,it makes the mechanical matching at the matrix interface better and changes the failure form from along-crystal fracture to quasi-destructive fracture.The problem of reducing plasticity while improving mechanical properties of magnesium matrix composites is solved.Therefore,the expected goal of this paper is achieved,and a new route is provided for the preparation of higher strength and high elastic modulus magnesium matrix composites.