The Effect Of Interfacial Behavior Of Mg₂B₂O₅Whisker Reinforced Magnesium Matrix Composite On The Mechanical Properties

ZnO and CuO were coated on the surface of magnesium borate whiskers by asol-gel technique in this paper. AZ31B magnesium matrix composite reinforced byMg₂B₂O₅whiskers were fabricated via vacuum-gas pressure infiltration process andthe volume fraction of the reinforcements were36%. According to kinds of coatings,composites were abbreviated and denoted as Mg₂B₂O₅w/AZ31B （non-coating）、ZnO/Mg₂B₂O₅w/AZ31B （ZnO coating） and CuO/Mg₂B₂O₅w/AZ31B （CuO coating）,respectively.The morphology and structure of magnesium borate whiskers were studied byscanning electronic microscope （SEM） and X-ray diffraction analysis （XRD）. Themicrostructure and interfacial reaction of composites were investigated by opticalmicroscope （OM）, scanning electronic microscope, electron probe microanalysis（EPMA） and transmission electron microscopy （TEM）. Mechanical properties of thecomposites were studied by tensile tests and hardness tests. The effects of coating andinterface on the tensile properties of composites were discussed. The tensilefractographs of composites were examined by scanning electronic microscope and thefracture mechanism was also analyzed.The results indicated that ZnO and CuO coating can be uniformly coated on thesurface of magnesium borate whiskers by means of sol-gel methods. At the elevatedtemperature of800C, ZnO and CuO coating did not reacted with magnesium matrixand not affected homogeneous distribution of magnesium borate whiskers in themagnesium matrix.The ZnO and CuO coatings changed the interfacial behavior of the composites.The interfacial reaction of Mg₂B₂O₅w/AZ31B composites took place between themagnesium and the adsorbed oxygen on the surface of the whiskers during thefabrication process. In the ZnO/Mg₂B₂O₅w/AZ31B and CuO/Mg₂B₂O₅w/AZ31Bcomposites, the interfacial reaction mainly took place between the coating andmagnesium matrix. The thermal exposure experiments indicated that the interfacial reaction in the Mg₂B₂O₅w/AZ31B composite was more serious, while theZnO/Mg₂B₂O₅w/AZ31B and CuO/Mg₂B₂O₅w/AZ31B composites had no interfacialreaction and their interfaces were stable.The interface of ZnO/Mg₂B₂O₅w/AZ31B composite can be classified into threetypes by the interfacial reaction products which were ZnO, Mg_0.85Zn_0.15O and MgO.The interfacial reaction products of CuO/Mg₂B₂O₅w/AZ31B were mainly composedof MgCu₂and MgZn₂phases. The orientation relationship between MgZn2andMg₂B₂O₅existed in a specific position.The hardnesses of ZnO/Mg₂B₂O₅w/AZ31B and CuO/Mg₂B₂O₅w/AZ31Bcomposites were increased and the hardness values of these two kinds of compositeswere very similar. The tensile strength and elongation to fracture ofZnO/Mg₂B₂O₅w/AZ31B and CuO/Mg₂B₂O₅w/AZ31B composites clearly increased.Meanwhile, the elastic modulus and the proof strength were also a little improved.ZnO coating was more effectively than CuO coating improved the mechanicalproperties.